Goodwill and Other Intangible Assets (Intangible Assets) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets, Net [Abstract]
Gross Balance		$ 728	$ 612
Accumulated Amortization		(441)	(399)
Net Balance		287	213
Indefinite-Lived Intangible Assets (Excluding Goodwill)		79	74
Indefinite- lived intangible assets, Amortization		0	0
Intangible Assets, Gross		807	686
Intangible Assets, Net		366	287
Land Use Rights [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Indefinite-Lived Intangible Assets (Excluding Goodwill)		45	47
Indefinite- lived intangible assets, Amortization		0	0
Water rights
Finite-Lived Intangible Assets, Net [Abstract]
Indefinite-Lived Intangible Assets (Excluding Goodwill)		20	17
Indefinite- lived intangible assets, Amortization		0	0
Other
Finite-Lived Intangible Assets, Net [Abstract]
Indefinite-Lived Intangible Assets (Excluding Goodwill)		14	10
Indefinite- lived intangible assets, Amortization		0	0
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Balance		416	396
Accumulated Amortization		(330)	(304)
Net Balance		86	92
Contractual payment rights
Finite-Lived Intangible Assets, Net [Abstract]
Gross Balance	[1]	65	56
Accumulated Amortization	[1]	(47)	(42)
Net Balance	[1]	18	14
Project Development Rights [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Gross Balance		57	4
Accumulated Amortization		(1)	(1)
Net Balance		56	3
Contracts
Finite-Lived Intangible Assets, Net [Abstract]
Gross Balance		92	53
Accumulated Amortization		(21)	(15)
Net Balance		71	38
Other
Finite-Lived Intangible Assets, Net [Abstract]
Gross Balance	[2]	98	103
Accumulated Amortization	[2]	(42)	(37)
Net Balance	[2]	$ 56	$ 66

[1] Represent legal rights to receive system reliability payments from the regulator.

[2] Includes management rights, sales concessions, gas extraction rights, and other individually insignificant intangible assets.