Commitments (Long-Term Purchase Commitments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Electricity Purchase Contracts
Long-Term Purchase Commitment [Line Items]
Purchases Under Long Term Contracts	$ 1,597	$ 827	$ 747
Purchase Obligation, Due in Next Twelve Months	699
Purchase Obligation, Due in Second Year	509
Purchase Obligation, Due in Third Year	406
Purchase Obligation, Due in Fourth Year	439
Purchase Obligation, Due in Fifth Year	459
Future Commitments Thereafter	5,110
Future Commitments Total	7,622
Fuel Purchase Contracts
Long-Term Purchase Commitment [Line Items]
Purchases Under Long Term Contracts	1,824	1,838	1,619
Purchase Obligation, Due in Next Twelve Months	1,385
Purchase Obligation, Due in Second Year	1,086
Purchase Obligation, Due in Third Year	756
Purchase Obligation, Due in Fourth Year	643
Purchase Obligation, Due in Fifth Year	568
Future Commitments Thereafter	2,601
Future Commitments Total	7,039
Other Purchase Contracts
Long-Term Purchase Commitment [Line Items]
Purchases Under Long Term Contracts	1,684	$ 1,671	$ 1,945
Purchase Obligation, Due in Next Twelve Months	1,551
Purchase Obligation, Due in Second Year	723
Purchase Obligation, Due in Third Year	538
Purchase Obligation, Due in Fourth Year	538
Purchase Obligation, Due in Fifth Year	529
Future Commitments Thereafter	1,745
Future Commitments Total	$ 5,624