v3.10.0.1

Retirement Benefits (Defined Contribution Savings Plans and Employee Stock Purchase Plan) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure
Share authorized to issue under the defined contribution savings plans (in shares)	16,800,000.0
Shares available for future contributions (in shares)	400,000
Contribution in shares (in shares)	400,000	500,000	600,000
Contribution in shares, Expense	$ 58	$ 56	$ 49
Contribution in cash, Expense	69	54	46
Total, Expense	$ 127	$ 110	$ 95
Percent of fair market value employees can purchase common stock under Employee Stock Purchase Plan	95.00%
Common stock issued to employees (in shares)	0	100,000	100,000
Common stock issued to employees value		$ 11	$ 10
Employee Stock [Member]
Defined Benefit Plan Disclosure
Common stock issued to employees value	$ 0	11	$ 11
B/E Aerospace [Member]
Defined Benefit Plan Disclosure
Contribution in cash, Expense	$ 11	$ 5

The amount of authorized shares under the defined contribution savings plans which are available for future contributions.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Total Company expense related to the defined contribution savings plans.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Defined contribution savings plans cash retirement contributions.

+ References

No definition available.

+ Details

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Namespace Prefix:	col_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of shares contributed to the defined contribution savings plans during the reporting period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The value of shares contributed to the defined contribution savings plans during the reporting period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Percent of fair market value employees are allowed to purchase the Company's common stock under the Employee Stock Purchase Plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	col_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of shares the Company is authorized to issue under the defined contribution savings plans.

+ References

No definition available.

+ Details

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Namespace Prefix:	col_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate change in value for stock issued during the period as a result of employee stock purchase plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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Balance Type:	credit
Period Type:	duration

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- Details

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ROCKWELL COLLINS INC 10-K