Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	$ 2,568		$ 2,475
Amounts Incurred	26	[1]	13	[2]
Amounts Settled	(5)	[3]	(14)	[4]
Accretion	128		120
Cash flow revisions	(16)	[5]	(26)	[6]
Ending balance	2,701		2,568
Electric Plant Nuclear Production Decommissioning
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	1,968		1,874
Amounts Incurred	0	[1]	0	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	100		94
Cash flow revisions	0	[5]	0	[6]
Ending balance	2,068		1,968
Electric Plant Steam, Hydro and Other Production Asbestos
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	177		192
Amounts Incurred	0	[1]	0	[2]
Amounts Settled	(5)	[3]	(14)	[4]
Accretion	8		8
Cash flow revisions	22	[5]	(9)	[6]
Ending balance	202		177
Electric Plant Wind Production
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	119		96
Amounts Incurred	26	[1]	12	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	7		4
Cash flow revisions	(6)	[5]	7	[6]
Ending balance	146		119
Electric Plant Electric Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	42		21
Amounts Incurred	0	[1]	0	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	2		1
Cash flow revisions	0	[5]	20	[6]
Ending balance	44		42
Electric Plant Miscellaneous
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	7		5
Amounts Incurred	0	[1]	0	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	0		0
Cash flow revisions	(7)	[5]	2	[6]
Ending balance	0		7
Natural Gas Plant Gas Transmission and Distribution
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	249		282
Amounts Incurred	0	[1]	0	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	11		13
Cash flow revisions	(24)	[5]	(46)	[6]
Ending balance	236		249
Natural Gas Plant Miscellaneous
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	4		4
Amounts Incurred	0	[1]	0	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	0		0
Cash flow revisions	(1)	[5]	0	[6]
Ending balance	3		4
Common and Other Property Common Miscellaneous
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	1		1
Amounts Incurred	0	[1]	0	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	0		0
Cash flow revisions	0	[5]	0	[6]
Ending balance	1		1
Non utility and other
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	1		0
Amounts Incurred	0	[1]	1	[2]
Amounts Settled	0	[3]	0	[4]
Accretion	0		0
Cash flow revisions	0	[5]	0	[6]
Ending balance	1		1
Nuclear Decommissioning Fund | Fair Value, Recurring [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Fund Investments	2,440		2,055
Legally restricted assets, for purposes of funding future nuclear decommissioning	$ 2,440		$ 2,100

[1] Amounts incurred related to the wind farms placed in service in 2019 for NSP-Minnesota (Lake Benton and Foxtail) and SPS (Hale).

[2] Amounts incurred related to the PSCo Rush Creek wind farm and Nicollet Projects community solar gardens, which were placed in service in 2018.

[3] Amounts settled related to asbestos abatement projects and closure of certain ash containment facilities.

[4] Amounts settled related to asbestos abatement projects and closure of certain 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. Changes in steam, hydro and other production AROs primarily related to the cost estimates to remediate ponds at production facilities. Changes in wind AROs were driven by new dismantling studies.

[6] In 2018, 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 increased discount rates. Changes in electric distribution AROs primarily related to increased labor costs.