Goodwill and Other Intangible Assets (Intangible Assets Acquired) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 121	$ 179
Computer Software, Intangible Asset [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 61	$ 67
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years	6 years
Other Intangible Assets [Member]
Indefinite-lived Intangible Assets [Line Items]
Other intangible assets acquired	$ 5	$ 11
Contracts
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 2	$ 50
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	35 years	24 years
Project Development Rights [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 8	$ 35
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	29 years	23 years
Emission allowances [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 22	$ 16
Transmission Rights [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired	$ 23