Leases (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020		Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 13	[1]	$ 14	[1]	$ 42	[2]	$ 38	[2]
Lessee, Operating Lease, Liability, to be Paid	611				611
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(141)				(141)
Operating Lease, Liability	470				470
Operating Lease, Liability, Current	(29)				(29)				$ (28)
Operating lease liabilities	441				441				$ 463
Short-term Lease, Cost					1		1
PPAs
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	13		13		40		35
Lessee, Operating Lease, Liability, to be Paid	555				555
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(125)				(125)
Operating Lease, Liability	430				430
Property, Plant and Equipment, Other Types
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	0	[3]	$ 1	[3]	2	[4]	$ 3	[4]
Lessee, Operating Lease, Liability, to be Paid	56				56
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(16)				(16)
Operating Lease, Liability	$ 40				$ 40

[1] PPA capacity payments are included in electric fuel and purchased power on the 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 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.