Fair Value (Nonrecurring Measurements) (Details) - USD ($)		2 Months Ended	3 Months Ended									6 Months Ended		8 Months Ended	12 Months Ended
		Feb. 28, 2017	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, 2015	Jun. 30, 2017	Jun. 30, 2016	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Other Asset Impairment Charges															$ 537,000,000	$ 1,096,000,000	$ 285,000,000
Goodwill impairment expense															0	0	317,000,000
Other non-operating expense																0
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax															(611,000,000)	(1,385,000,000)	0
Impairment Expense Pre Tax Total			$ 277,000,000	$ 2,000,000	$ 90,000,000	$ 168,000,000	$ 623,000,000	$ 79,000,000	$ 235,000,000	$ 159,000,000
DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Goodwill impairment expense											$ 317,000,000
Sul Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax													$ 602,000,000
Estimate of Fair Value Measurement [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring			64,000,000												64,000,000
Long Lived Assets Held And Used [Member] | DPL Peaking Generation [Domain]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring							2,000,000		5,000,000				5,000,000			2,000,000
Long Lived Assets Held And Used [Member] | Laurel Mountain [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring			33,000,000												33,000,000
Other Asset Impairment Charges	[1]														121,000,000
Long Lived Assets Held And Used [Member] | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring			20,000,000								$ 70,000,000				20,000,000		$ 70,000,000
Other Asset Impairment Charges	[1]														37,000,000
Long Lived Assets Held And Used [Member] | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Other Asset Impairment Charges	[1]	$ 66,000,000											235,000,000			624,000,000
Long Lived Assets Held And Used [Member] | Buffalo Gap [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring							36,000,000									36,000,000
Other Asset Impairment Charges	[1]													$ 77,000,000
Long Lived Assets Held And Used [Member] | Other Subsidiaries [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Other Asset Impairment Charges															18,000,000
Long Lived Assets Held And Used [Member] | buffalo gap II [Member] [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring							92,000,000									92,000,000
Other Asset Impairment Charges	[1]									159,000,000
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Laurel Mountain [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		0												0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Laurel Mountain [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		0												0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Laurel Mountain [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		33,000,000												33,000,000
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Kilroot [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		0												0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Kilroot [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		0												0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Kilroot [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		20,000,000												20,000,000
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | DPL Subsidiary | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]	0					0		0				0			0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | DPL Subsidiary | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]	0					60,000,000		0				0			60,000,000
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | DPL Subsidiary | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]	11,000,000					103,000,000		89,000,000				89,000,000			103,000,000
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Buffalo Gap [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]													0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Buffalo Gap [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]													0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Buffalo Gap [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]													36,000,000
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Other Subsidiaries [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring			0												0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Other Subsidiaries [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring			0												0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | Other Subsidiaries [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring			0												0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | buffalo gap II [Member] [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]									0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | buffalo gap II [Member] [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]									0
Long Lived Assets Held And Used [Member] | Estimate of Fair Value Measurement [Member] | buffalo gap II [Member] [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]									92,000,000
Long Lived Assets Held And Used [Member] | Reported Value Measurement [Member] | Laurel Mountain [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1],[2]		154,000,000												154,000,000
Long Lived Assets Held And Used [Member] | Reported Value Measurement [Member] | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1],[2]		69,000,000												69,000,000
Long Lived Assets Held And Used [Member] | Reported Value Measurement [Member] | DPL Subsidiary
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1],[2]	$ 77,000,000					$ 787,000,000		324,000,000				324,000,000			$ 787,000,000
Long Lived Assets Held And Used [Member] | Reported Value Measurement [Member] | Buffalo Gap [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1],[2]													$ 113,000,000
Long Lived Assets Held And Used [Member] | Reported Value Measurement [Member] | Other Subsidiaries [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring			18,000,000												18,000,000
Long Lived Assets Held And Used [Member] | Reported Value Measurement [Member] | buffalo gap II [Member] [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1],[2]									$ 251,000,000
Long Lived Assets Held For Sale [Member] | DPL Peaking Generation [Domain]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Other Asset Impairment Charges	[1]														109,000,000
Long Lived Assets Held For Sale [Member] | Kazakhstan [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Other Asset Impairment Charges						94,000,000
Long Lived Assets Held For Sale [Member] | Kazakhstan Hydro [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Other Asset Impairment Charges												$ 92,000,000
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | DPL Peaking Generation [Domain] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		0												0
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | DPL Peaking Generation [Domain] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		237,000,000												237,000,000
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | DPL Peaking Generation [Domain] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]		0												0
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Kazakhstan [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring						0
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Kazakhstan [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring						29,000,000
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Kazakhstan [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring						0
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Kazakhstan Hydro [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring					0							0
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Kazakhstan Hydro [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring					92,000,000							92,000,000
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Kazakhstan Hydro [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring					0							0
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Sul Subsidiary [Member] | Level 1
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring									0				0
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Sul Subsidiary [Member] | Level 2
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring									470,000,000				470,000,000
Long Lived Assets Held For Sale [Member] | Estimate of Fair Value Measurement [Member] | Sul Subsidiary [Member] | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring									0				0
Long Lived Assets Held For Sale [Member] | Reported Value Measurement [Member] | DPL Peaking Generation [Domain]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1],[2]		$ 346,000,000												$ 346,000,000
Long Lived Assets Held For Sale [Member] | Reported Value Measurement [Member] | Kazakhstan [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring						$ 171,000,000
Long Lived Assets Held For Sale [Member] | Reported Value Measurement [Member] | Kazakhstan Hydro [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring					$ 190,000,000							190,000,000
Long Lived Assets Held For Sale [Member] | Reported Value Measurement [Member] | Sul Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets, Fair Value Disclosure, Nonrecurring									$ 1,581,000,000				$ 1,581,000,000
Discontinued Operations, Held-for-sale [Member] | Sul Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Other Asset Impairment Charges	[1]											$ 783,000,000

[1] See Note 19—Asset Impairment Expense for further information.

[2] Represents the carrying values at the dates of measurement, before fair value adjustment.