Commitments and Contingencies, Leases (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Maximum Length - Short-Term Leases		12 months
Operating Lease, Weighted Average Discount Rate, Percent		4.40%
Short-term Lease, Cost		$ 1	$ 2	$ 1
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		550	548
Operating Lease, Right-of-Use Asset, Accumulated Depreciation		(58)	(26)
Operating lease right-of-use assets		492	522
Lease, Cost [Abstract]
Operating Lease, Cost	[1]	51	53	59
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021		49
2022		49
2023		49
2024		49
2025		49
Thereafter		402
Total minimum obligation		647
Interest component of obligation		(156)
Present value of minimum obligation		491
Less current portion		(28)	(27)
Operating Lease, Liability, Noncurrent		$ 463	495
Weighted-average remaining lease term in years		13 years
Property, Plant and Equipment, Other Types [Member]
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		$ 50	48
Lease, Cost [Abstract]
Operating Lease, Cost	[2]	3	5	8
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021		3
2022		3
2023		3
2024		3
2025		3
Thereafter		43
Total minimum obligation		58
Interest component of obligation		(17)
Present value of minimum obligation		41
Purchased Power Agreements
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		500	500
Lease, Cost [Abstract]
Operating Lease, Cost		48	$ 48	$ 51
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	[3],[4]	46
2022	[3],[4]	46
2023	[3],[4]	46
2024	[3],[4]	46
2025	[3],[4]	46
Thereafter	[3],[4]	359
Total minimum obligation	[3],[4]	589
Interest component of obligation	[3],[4]	(139)
Present value of minimum obligation	[3],[4]	$ 450

[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.

[2] Includes short-term lease expense of $1 million, $2 million and $1 million for 2020, 2019 and 2018, respectively.

[3] Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs.

[4] PPA operating leases contractually expire at various dates through 2033.