Commitments and Contingencies - Leases (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021		Jun. 30, 2020		Jun. 30, 2021		Jun. 30, 2020		Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 29	[1]	$ 28	[1]	$ 58	[2]	$ 56	[2]
Finance Lease, Right-of-Use Asset, Amortization	2		2		4		3
Finance Lease, Interest Expense	4		4		8		9
Finance Lease, Cost	6		6		12		12
Lessee, Operating Lease, Liability, Payments, Due	554				554
Total minimum obligation	472				472
Interest component of obligation	(72)				(72)
Finance Lease, Liability, Undiscounted Excess Amount	(344)				(344)
Operating Lease, Liability	482				482
Finance Lease, Liability	128				128
Less current portion	(98)				(98)				$ (97)
Less current portion	(5)				(5)
Operating lease liabilities	384				384				$ 432
Noncurrent operating and finance lease liabilities	123				123
Short-term Lease, Cost					1		1
PPAs
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	26		25		51		49
Lessee, Operating Lease, Liability, Payments, Due	493				493
Interest component of obligation	(65)				(65)
Operating Lease, Liability	428				428
Other
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	3	[3]	$ 3	[3]	7	[4]	$ 7	[4]
Lessee, Operating Lease, Liability, Payments, Due	61				61
Interest component of obligation	(7)				(7)
Operating Lease, Liability	$ 54				$ 54

[1] PPA capacity payments are included in electric fuel and purchased power on the consolidated statements of income. Expense for other operating leases is included in O&M expense and electric fuel and purchased power.

[2] PPA capacity payments are included in electric fuel and purchased power on the consolidated statements of income. Expense for other operating leases is included in O&M expense and electric fuel and purchased power.

[3] Includes immaterial short-term lease expense for 2021 and 2020.

[4] Includes short-term lease expense of $1 million for 2021 and 2020, respectively.