Commitments and Contingencies, Asset Retirement Obligations (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		$ 324	[1]	$ 338
Amounts Incurred	[2]	26
Amounts Settled	[3]	(3)
Accretion		14		16
Cash Flow Revisions		38	[4]	(30)	[5]
Ending balance		399		324	[1]
Electric Plant Steam and Other Production Ash Containment
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		100	[1]	102
Amounts Incurred	[2]	0
Amounts Settled	[3]	0
Accretion		4		5
Cash Flow Revisions		33	[4]	(7)	[5]
Ending balance		137		100	[1]
Electric Plant Wind Production
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		16	[1]	14
Amounts Incurred	[2]	26
Amounts Settled	[3]	(3)
Accretion		1		1
Cash Flow Revisions		0	[4]	1	[5]
Ending balance		40		16	[1]
Electric Plant Electric Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		14	[1]	13
Amounts Incurred	[2]	0
Amounts Settled	[3]	0
Accretion		1		1
Cash Flow Revisions		0	[4]	0	[5]
Ending balance		15		14	[1]
Electric Plant Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		0	[1]	3
Accretion				0
Cash Flow Revisions	[5]			(3)
Ending balance	[1]			0
Natural Gas Plant Gas Transmission and Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		190	[1]	201
Amounts Incurred	[2]	0
Amounts Settled	[3]	0
Accretion		8		9
Cash Flow Revisions		5	[4]	(20)	[5]
Ending balance		203		190	[1]
Natural Gas Plant Other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		3	[1]	4
Amounts Incurred	[2]	0
Amounts Settled	[3]	0
Accretion		0		0
Cash Flow Revisions		0	[4]	(1)	[5]
Ending balance		3		3	[1]
Common and Other Property Common Miscellaneous
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		1	[1]	1
Amounts Incurred	[2]	0
Amounts Settled	[3]	0
Accretion		0		0
Cash Flow Revisions		0	[4]	0	[5]
Ending balance		$ 1		$ 1	[1]

[1] There were no ARO amounts incurred or settled in 2019

[2] Amounts incurred related to the Cheyenne Ridge wind farm placed in service in 2020.

[3] Amounts settled related to removal of wind facilities.

[4] In 2020, AROs were revised for changes in timing and estimates of cash flows. Revisions in steam, hydro, and other production AROs primarily related to changes in cost estimates for remediation ash containment facilities.

[5] In 2019, AROs were revised for changes in timing and estimates of cash flows. Changes in gas transmission and distribution AROs were primarily related to increased gas line mileage and number of services, which were more than offset by decreased inflation rates. Revisions in steam, hydro, and other production AROs primarily related to changes in cost estimates for pond remediation.