Goodwill and Other Intangible Assets (Intangible Assets Acquired) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 179	$ 112
Computer Software, Intangible Asset [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 67	$ 17
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years	7 years
Other Intangible Assets [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 8
Other intangible assets acquired	$ 11
Contracts
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 50	$ 34
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	24 years	25 years
Project Development Rights [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 35	$ 53
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	23 years	30 years
Emission allowances [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 16