Non Lease PPAs (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Capacity
Purchased Power Agreements (PPAs) [Abstract]
Purchased power expense		$ 86	$ 131	$ 168
Estimated Future Payments Under PPAs [Abstract]
2020		70
2021		78
2022		77
2023		79
2024		74
Thereafter		56
Total		434
Energy
Purchased Power Agreements (PPAs) [Abstract]
Purchased power expense		102	$ 105	$ 100
Estimated Future Payments Under PPAs [Abstract]
2020	[1]	110
2021	[1]	157
2022	[1]	173
2023	[1]	177
2024	[1]	182
Thereafter	[1]	146
Total	[1]	$ 945

[1] Excludes contingent energy payments for renewable energy PPAs.