Benefit Obligations - Fair Value of the U.S. Pension Plans Assets by Asset Class (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Long duration fixed income
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	85.00%
U.S. equity
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	9.00%
Non-U.S. equity
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	6.00%
Post-retirement Benefits \| Investments measured at net asset value:
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 15	$ 21
Post-retirement Benefits \| Insurance Contracts \| Investments measured at net asset value:
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15	21
Non-US \| Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 15	$ 20	$ 18
Plan asset allocations	100.00%	100.00%
Non-US \| Pension Plan \| Investments measured at net asset value:
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 15	$ 20
Non-US \| Pension Plan \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	7.00%	10.00%
Non-US \| Pension Plan \| Debt Securities \| Investments measured at net asset value:
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1	$ 2
Non-US \| Pension Plan \| Asset Allocation \| Investments measured at net asset value:
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3	$ 5
Non-US \| Pension Plan \| Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	74.00%	63.00%
Non-US \| Pension Plan \| Insurance Contracts \| Investments measured at net asset value:
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 11	$ 13
U.S. \| Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 687	$ 932	927
Plan asset allocations	100.00%	100.00%
U.S. \| Pension Plan \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Other plan assets, net	$ (1)	$ (3)
Fair value of plan assets	687	932
U.S. \| Pension Plan \| Level 1 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	0
U.S. \| Pension Plan \| Level 2 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	83	114
U.S. \| Pension Plan \| Level 3 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. \| Pension Plan \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	604	815
U.S. \| Pension Plan \| US Government Debt Securities And Derivative Instruments \| Level 1 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	0
U.S. \| Pension Plan \| US Government Debt Securities And Derivative Instruments \| Level 2 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	83	114
U.S. \| Pension Plan \| US Government Debt Securities And Derivative Instruments \| Level 3 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. \| Pension Plan \| US Government Debt Securities And Derivative Instruments \| Total \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	84	114
U.S. \| Pension Plan \| U.S. Government debt securities \| Level 1 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. \| Pension Plan \| U.S. Government debt securities \| Level 2 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	83	114
U.S. \| Pension Plan \| U.S. Government debt securities \| Level 3 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. \| Pension Plan \| U.S. Government debt securities \| Total \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	83	114
U.S. \| Pension Plan \| Derivative instruments \| Level 1 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	0
U.S. \| Pension Plan \| Derivative instruments \| Level 2 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. \| Pension Plan \| Derivative instruments \| Level 3 \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. \| Pension Plan \| Derivative instruments \| Total \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1	$ 0
U.S. \| Pension Plan \| Real estate
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	9.00%	6.00%
U.S. \| Pension Plan \| Real estate \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 62	$ 51
U.S. \| Pension Plan \| Private equity \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1
U.S. \| Pension Plan \| Multi-strategy hedge funds \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50	50
U.S. \| Pension Plan \| Cash equivalents \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35	35
U.S. \| Pension Plan \| Long duration fixed income \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	282	383
U.S. \| Pension Plan \| U.S. equity \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	106	172
U.S. \| Pension Plan \| Non-U.S. equity \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	49	89
U.S. \| Pension Plan \| Emerging market equity \| Investments measured at net asset value: \| Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 20	$ 34
U.S. \| Pension Plan \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	53.00%	53.00%
U.S. \| Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 15	$ 21	$ 206
Plan asset allocations	100.00%	100.00%
U.S. \| Post-retirement Benefits \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan asset allocations	85.00%	85.00%

Avaya Holdings Corp. 10-K