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		3.90%
Short-term Lease, Cost		$ 1	$ 2	$ 1
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		659	654
Operating Lease, Right-of-Use Asset, Accumulated Depreciation		(159)	(80)
Operating lease right-of-use assets		500	574
Finance Lease, Assets and Liabilities, Lessee [Abstract]
Finance Lease, Right-of-Use Asset, Gross		222	221
Finance Lease, Right-of-Use Asset, Accumulated Depreciation		(90)	(82)
Finance Lease, Right-of-Use Asset		132	139
Lease, Cost [Abstract]
Operating Lease, Cost	[1]	113	112	111
Finance Lease, Right-of-Use Asset, Amortization		7	6	6
Finance Lease, Interest Expense		18	19	19
Finance Lease, Cost		25	25	25
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021		116
2022		99
2023		80
2024		73
2025		68
Thereafter		175
Total minimum obligation		611
Interest component of obligation		(82)
Present value of minimum obligation		529
Less current portion		(97)	(86)
Operating lease liabilities		$ 432	518
Operating Lease, Weighted Average Remaining Lease Term		7 years 1 month 6 days
Lessee, Finance Lease, Description [Abstract]
2021		$ 24
2022		21
2023		20
2024		20
2025		19
Thereafter		381
Total minimum obligation		485
Interest component of obligation		(352)
Present value of minimum obligation		133
Less current portion		(7)
Noncurrent operating and finance lease liabilities		$ 126
Finance Lease, Weighted Average Remaining Lease Term		38 years
Property, Plant and Equipment, Other Types [Member]
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		$ 68	69
Lease, Cost [Abstract]
Operating Lease, Cost	[2]	13	14	14
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021		15
2022		15
2023		10
2024		10
2025		5
Thereafter		12
Total minimum obligation		67
Interest component of obligation		(8)
Present value of minimum obligation		59
Gas Storage Facilities [Member]
Finance Lease, Assets and Liabilities, Lessee [Abstract]
Finance Lease, Right-of-Use Asset, Gross		201	200
Gas Pipeline
Finance Lease, Assets and Liabilities, Lessee [Abstract]
Finance Lease, Right-of-Use Asset, Gross		21	21
Purchased Power Agreements
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross		591	585
Lease, Cost [Abstract]
Operating Lease, Cost		100	$ 98	$ 97
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	[3],[4]	101
2022	[3],[4]	84
2023	[3],[4]	70
2024	[3],[4]	63
2025	[3],[4]	63
Thereafter	[3],[4]	163
Total minimum obligation	[3],[4]	544
Interest component of obligation	[3],[4]	(74)
Present value of minimum obligation	[3],[4]	$ 470
WYCO, Inc. [Member]
Lessee, Finance Lease, Description [Abstract]
Equity Method Investment, Ownership Percentage		50.00%

[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] 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 2032.