Goodwill and Other Intangible Assets (Intangible Assets Acquired) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 454	$ 121
Computer Software, Intangible Asset [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 35	$ 61
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	4 years	5 years
Other Intangible Assets [Member]
Indefinite-lived Intangible Assets [Line Items]
Other intangible assets acquired	$ 22	$ 5
Contracts
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 28	$ 2
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	20 years	35 years
Project Development Rights [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 109	$ 8
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	30 years	29 years
Emission allowances [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 56	$ 22
Transmission Rights [Member]
Indefinite-lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 23
Compensation from Concession Agreement
Indefinite-lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	12 years
Transmission Rights [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired	$ 20
Compensation from Concession Agreement
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired	$ 184