Commitments and Contingencies - Leases (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2023		Sep. 30, 2022		Sep. 30, 2023		Sep. 30, 2022		Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 28	[1]	$ 27	[1]	$ 86	[2]	$ 80	[2]
Lessee, Operating Lease, Liability, to be Paid	423				423
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(92)				(92)
Operating Lease, Liability	331				331
Operating Lease, Liability, Current	(98)				(98)				$ (98)
Operating lease liabilities	233				233				$ 256
Purchased Power Agreements
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	25		25		74		74
Lessee, Operating Lease, Liability, to be Paid	244				244
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(11)				(11)
Operating Lease, Liability	233				233
Property, Plant and Equipment, Other Types
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	3	[3]	$ 2	[3]	12	[4]	6	[4]
Lessee, Operating Lease, Liability, to be Paid	179				179
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(81)				(81)
Operating Lease, Liability	$ 98				98
Short-term Lease, Cost					$ 3		$ 2

[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 both 2023 and 2022.

[4] Includes short-term lease expense of $3 million and $2 million for 2023 and 2022, respectively.