Condensed Consolidating Financial Information - Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 994	$ 1,437	$ 1,164	$ 1,247	$ 1,107	$ 1,184	$ 904	$ 1,123	$ 4,842	$ 4,318	$ 3,870
Cost of sales, excluding depreciation expense									(2,932)	(2,281)	(2,028)
Gross margin									1,910	2,037	1,842
Operating and maintenance expense									(995)	(940)	(839)
Depreciation expense									(811)	(689)	(587)
Impairments									(148)	(858)	(99)
Loss on sale of assets, net	15	78	29						(122)	(1)	(1)
General and administrative expense									(189)	(161)	(128)
Acquisition and integration costs									(57)	(11)	(124)
Other									0	(17)	0
Operating income (loss)	(239)	58	(182)	(49)	34	(117)	(702)	145	(412)	(640)	64
Bankruptcy reorganization items									494	(96)	0
Earnings from unconsolidated investments									8	7	1
Equity in losses from investments in affiliates									0	0	0
Interest expense									(616)	(625)	(546)
Loss on early extinguishment of debt (Note 13)									(79)	0	0
Other income and expense, net									67	65	54
Loss before income taxes									(538)	(1,289)	(427)
Income tax benefit (Note 14)									610	45	474
Net income (loss)	(95)	(133)	(296)	596	(182)	(249)	(803)	(10)	72	(1,244)	47
Less: Net loss attributable to noncontrolling interest									(4)	(4)	(3)
Net Income attributable to Dynegy Inc.	$ (95)	$ (137)	$ (302)	$ 592	$ (186)	$ (254)	$ (807)	$ (15)	76	(1,240)	50
Eliminations
Condensed Financial Statements, Captions [Line Items]
Revenues									(137)	(92)	(163)
Cost of sales, excluding depreciation expense									137	92	163
Gross margin									0	0	0
Operating and maintenance expense									0	0	0
Depreciation expense									0	0	0
Impairments									0	0	0
Loss on sale of assets, net									0	0	0
General and administrative expense									0	0	0
Acquisition and integration costs									0	0	0
Other										0
Operating income (loss)									0	0	0
Bankruptcy reorganization items									0	0
Earnings from unconsolidated investments									0	0	0
Equity in losses from investments in affiliates									(824)	715	(476)
Interest expense									14	5	2
Loss on early extinguishment of debt (Note 13)									0
Other income and expense, net									(14)	(5)	(2)
Loss before income taxes									(824)	715	(476)
Income tax benefit (Note 14)									0	0	0
Net income (loss)									(824)	715	(476)
Less: Net loss attributable to noncontrolling interest									0	0	0
Net Income attributable to Dynegy Inc.									(824)	715	(476)
Parent \| Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Revenues									0	0	0
Cost of sales, excluding depreciation expense									0	0	0
Gross margin									0	0	0
Operating and maintenance expense									0	0	0
Depreciation expense									0	0	0
Impairments									0	0	0
Loss on sale of assets, net									0	(2)	0
General and administrative expense									(28)	(7)	(6)
Acquisition and integration costs									(54)	(10)	0
Other										0
Operating income (loss)									(82)	(19)	(6)
Bankruptcy reorganization items									(18)	0
Earnings from unconsolidated investments									0	0	0
Equity in losses from investments in affiliates									824	(715)	476
Interest expense									(597)	(538)	(475)
Loss on early extinguishment of debt (Note 13)									(79)
Other income and expense, net									28	32	55
Loss before income taxes									76	(1,240)	50
Income tax benefit (Note 14)									0	0	0
Net income (loss)									76	(1,240)	50
Less: Net loss attributable to noncontrolling interest									0	0	0
Net Income attributable to Dynegy Inc.									76	(1,240)	50
Guarantor Subsidiaries \| Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Revenues									4,557	3,942	3,508
Cost of sales, excluding depreciation expense									(2,790)	(2,112)	(1,874)
Gross margin									1,767	1,830	1,634
Operating and maintenance expense									(881)	(796)	(717)
Depreciation expense									(757)	(612)	(505)
Impairments									(148)	(858)	(74)
Loss on sale of assets, net									(123)	1	(1)
General and administrative expense									(155)	(148)	(116)
Acquisition and integration costs									(3)	(1)	(124)
Other										(9)
Operating income (loss)									(300)	(593)	97
Bankruptcy reorganization items									512	(96)
Earnings from unconsolidated investments									8	7	1
Equity in losses from investments in affiliates									0	0	0
Interest expense									(20)	(83)	(69)
Loss on early extinguishment of debt (Note 13)									0
Other income and expense, net									53	38	1
Loss before income taxes									253	(727)	30
Income tax benefit (Note 14)									610	45	472
Net income (loss)									863	(682)	502
Less: Net loss attributable to noncontrolling interest									(4)	(4)	(3)
Net Income attributable to Dynegy Inc.									867	(678)	505
Non-Guarantor Subsidiaries \| Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Revenues									422	468	525
Cost of sales, excluding depreciation expense									(279)	(261)	(317)
Gross margin									143	207	208
Operating and maintenance expense									(114)	(144)	(122)
Depreciation expense									(54)	(77)	(82)
Impairments									0	0	(25)
Loss on sale of assets, net									1	0	0
General and administrative expense									(6)	(6)	(6)
Acquisition and integration costs									0	0	0
Other										(8)
Operating income (loss)									(30)	(28)	(27)
Bankruptcy reorganization items									0	0
Earnings from unconsolidated investments									0	0	0
Equity in losses from investments in affiliates									0	0	0
Interest expense									(13)	(9)	(4)
Loss on early extinguishment of debt (Note 13)									0
Other income and expense, net									0	0	0
Loss before income taxes									(43)	(37)	(31)
Income tax benefit (Note 14)									0	0	2
Net income (loss)									(43)	(37)	(29)
Less: Net loss attributable to noncontrolling interest									0	0	0
Net Income attributable to Dynegy Inc.									$ (43)	$ (37)	$ (29)

DYNEGY INC. 10-K