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	$ 14	[1]	$ 13	[1]	$ 28	[2]	$ 25	[2]
Lessee, Operating Lease, Liability, to be Paid	624				624
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(146)				(146)
Operating Lease, Liability	478				478
Operating Lease, Liability, Current	(29)				(29)				$ (28)
Operating lease liabilities	449				449				$ 463
Short-term Lease, Cost					1		1
PPAs
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	13		12		26		23
Lessee, Operating Lease, Liability, to be Paid	567				567
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(130)				(130)
Operating Lease, Liability	437				437
Property, Plant and Equipment, Other Types
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	1	[3]	$ 1	[3]	2	[4]	$ 2	[4]
Lessee, Operating Lease, Liability, to be Paid	57				57
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(16)				(16)
Operating Lease, Liability	$ 41				$ 41

[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.