Leases (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	[1]	$ 14	$ 12
Lessee, Operating Lease, Liability, to be Paid		636
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		(151)
Operating Lease, Liability		485
Operating Lease, Liability, Current		(28)		$ (28)
Operating lease liabilities		457		$ 463
PPAs
Lessee, Lease, Description [Line Items]
Operating Lease, Cost		13	11
Lessee, Operating Lease, Liability, to be Paid		578
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		(134)
Operating Lease, Liability		444
Property, Plant and Equipment, Other Types
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	[2]	1	$ 1
Lessee, Operating Lease, Liability, to be Paid		58
Lessee, Operating Lease, Liability, Undiscounted Excess Amount		(17)
Operating Lease, Liability		$ 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] Includes immaterial short-term lease expense for 2021 and 2020.