Asset Impairment Expense (Impairment of Long-Lived Assets Held and Used by Asset) (Details) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Asset Impairment Expense [Line Items]
Asset impairment expense	$ (69)	$ (116)	$ (42)	$ (74)	$ (92)	$ (185)	$ (208)	$ (537)
Impairment of Long-Lived Assets Held-for-use						185	208	537
Kilroot and Ballylumford [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use						115	0	37
Hawaii Subsidiary [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use						60	0	0
Shady Point [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use						0	157	0
Nejapa [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use						0	37	0
DPL Subsidiary [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use						0	0	175
Laurel Mountain [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use						0	0	121
Kazakhstan Hydro [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets to be Disposed of						0	0	92
Kazakhstan [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets to be Disposed of						0	0	94
Other
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use						$ 10	$ 14	$ 18