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, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Asset Impairment Expense [Line Items]
Asset impairment expense	$ (42)	$ (74)	$ (92)	$ (277)	$ (90)	$ (168)	$ (208)	$ (537)	$ (1,096)
Impairment of Long-Lived Assets Held-for-use							208	537	1,096
Shady Point [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							157	0	0
Nejapa [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							37	0	0
DPL Subsidiary [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							0	175	859
Laurel Mountain [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							0	121	0
Kazakhstan Hydro [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets to be Disposed of							0	92	0
Kazakhstan [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets to be Disposed of							0	94	0
Kilroot [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							0	37	0
buffalo gap II [Member] [Member]
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							0	0	159
Buffalo Gap I
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							0	0	77
Other
Asset Impairment Expense [Line Items]
Impairment of Long-Lived Assets Held-for-use							$ 14	$ 18	$ 1