Income Taxes (Details) - USD ($)		1 Months Ended	3 Months Ended				12 Months Ended
		Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2015	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Federal Tax Reform [Abstract]
Tax Cuts and Jobs Act of 2017, Corporate Federal Tax Rate		21.00%					21.00%
Tax Cuts and Jobs Act of 2017, Net Operating Loss Deduction Limitation, Percent of Taxable income							80.00%
Reclassification of deferred taxes to regulatory liabilities, grossed-up for taxes								$ 3,800,000,000
Regulatory liability, customer refunds, weighted average period								30 years
Provisional income tax expense for tax reform								$ 23,000,000
Federal Tax Loss Carryback Claims [Abstract]
Number Of Years Of Tax Loss Carryback Period							two
Tax Adjustments, Settlements, and Unusual Provisions												$ 5,000,000	$ 17,000,000	$ 12,000,000	$ 15,000,000
Tax Audits [Abstract]
Unrecognized Tax Benefits, Interest on Income Taxes Accrued																$ 0	$ 0	$ (3,000,000)	$ 0
Unrecognized Tax Benefits, Interest on Income Taxes Accrued							$ 0	(3,000,000)		$ 3,000,000
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions																28,000,000	20,000,000
Unrecognized tax benefit — Temporary tax positions																9,000,000	19,000,000
Total unrecognized tax benefit		$ 39,000,000	$ 37,000,000				39,000,000	134,000,000		121,000,000		121,000,000				37,000,000	39,000,000	134,000,000	$ 121,000,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at Jan. 1							39,000,000	134,000,000		121,000,000
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions							9,000,000	6,000,000		8,000,000
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions							(4,000,000)	(4,000,000)		0
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions							2,000,000	15,000,000		10,000,000
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions							(4,000,000)	(105,000,000)		(5,000,000)
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities							(5,000,000)	(7,000,000)		0
Balance at Dec. 31		$ 39,000,000	$ 37,000,000				$ 37,000,000	$ 39,000,000		$ 134,000,000		$ 121,000,000
Tax Benefits Associated With NOL And Tax Credit Carryforwards [Abstract]
NOL and tax credit carryforwards																(35,000,000)	(31,000,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards																(24,000,000)	(13,000,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible																28,000,000
Unrecognized Tax Benefits, Income Tax Penalties Accrued																0	0	$ 0
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent							21.00%	35.00%	[1]	35.00%	[1]
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent							5.00%	4.10%	[1]	4.10%	[1]
Effective Income Tax Rate Reconciliation, Tax Credit, Percent							(5.20%)	(4.70%)	[1]	(3.40%)	[1]
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items, Percent							(2.00%)	(1.00%)	[1]	(0.80%)	[1]
Tax reform, Percent	[2]						0.60%	0.00%	[1]	0.00%	[1]
Regulatory differences - effects of rate changes, Percent	[3]						(5.80%)	(0.10%)	[1]	(0.10%)	[1]
Regulatory differences - other utility plant items, Percent							(1.00%)	(0.70%)	[1]	(0.50%)	[1]
Effective Income Tax Rate Reconciliation Change In Unrecognized Tax Benefits, Percent							0.40%	(0.60%)	[1]	0.20%	[1]
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.00%	1.40%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent							(0.40%)	(1.30%)	[1]	(0.40%)	[1]
Effective Income Tax Rate Reconciliation, Percent							12.60%	32.10%	[1]	34.10%	[1]
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)							$ (34,000,000)	$ 1,000,000		$ (3,000,000)
Current State and Local Tax Expense (Benefit)							8,000,000	(11,000,000)		(4,000,000)
Current Change In Unrecognized Tax Expense (Benefit)							(6,000,000)	(83,000,000)		6,000,000
Deferred Federal Income Tax Expense (Benefit)							122,000,000	460,000,000		477,000,000
Deferred State and Local Income Tax Expense (Benefit)							85,000,000	107,000,000		112,000,000
Deferred Change In Unrecognized Tax Expense (Benefit)							11,000,000	73,000,000		(2,000,000)
Deferred investment tax credits							(5,000,000)	(5,000,000)		(5,000,000)
Income Tax Expense (Benefit)							181,000,000	542,000,000		581,000,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred tax expense (benefit) excluding selected items							320,000,000	(2,939,000,000)		631,000,000
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities							(102,000,000)	3,583,000,000		(45,000,000)
Other Comprehensive Income (Loss), Tax							0	(4,000,000)		1,000,000
Deferred Income Tax Expense (Benefit)							$ 218,000,000	640,000,000		$ 587,000,000
Deferred Tax Liabilities, Gross [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment																5,082,000,000	4,960,000,000
Deferred Tax Liabilities, Regulatory Assets																599,000,000	565,000,000
Pension expense																178,000,000	199,000,000
Deferred Tax Liabilities, Other																64,000,000	57,000,000
Deferred Tax Liabilities, Gross																5,923,000,000	5,781,000,000
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets Regulatory Liabilities																879,000,000	886,000,000
Deferred Tax Assets Tax credit carryforward																642,000,000	607,000,000
Deferred Tax Assets, Operating Loss Carryforwards																51,000,000	293,000,000
Deferred Tax Assets, Valuation Allowance																(79,000,000)	(77,000,000)
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits																124,000,000	132,000,000
Deferred Tax Assets Deferred Investment Tax Credits																16,000,000	17,000,000
Deferred Tax Assets Rate Refund																60,000,000	10,000,000
Deferred Tax Assets, Other																65,000,000	68,000,000
Deferred Tax Assets, Net of Valuation Allowance																1,758,000,000	1,936,000,000
Deferred Tax Liabilities, Net																4,165,000,000	3,845,000,000
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Operating Loss Carryforwards																0	1,072,000,000
Tax Credit Carryforward, Amount																553,000,000	517,000,000
Tax Credit Carryforward, Valuation Allowance																(5,000,000)	(5,000,000)
Carryforward expiration date range, low							2021
Carryforward expiration date range, high							2038
Tax years under examination, Concluded					2012 and 2013
Tax years under examination			2014 - 2016			2012 and 2013									2010 and 2011
Year of carryback claim under examination															2009
Potential Tax Adjustments			$ 0
Colorado
Tax Audits [Abstract]
Earliest year subject to examination							2009
Minnesota
Tax Audits [Abstract]
Tax years under examination, Concluded			2010 - 2014
Earliest year subject to examination							2009
Potential Tax Adjustments				$ 0
Texas
Tax Audits [Abstract]
Earliest year subject to examination							2010
Wisconsin
Tax Audits [Abstract]
Tax years under examination, Concluded				2012 - 2013
Earliest year subject to examination							2014
Tax years under examination			2014 - 2016
Potential Tax Adjustments			$ 0	$ 0
State and Local Jurisdiction
Tax Audits [Abstract]
Operating Loss Carryforwards																1,104,000,000	1,592,000,000
Operating Loss Carryforwards, Valuation Allowance																(50,000,000)	(55,000,000)
Tax Credit Carryforward Net Of Federal Detriment	[4]															89,000,000	90,000,000
Valuation Allowance for Tax Credit Carryforward Net of Federal Benefit	[5]															(69,000,000)	(68,000,000)
Federal detriment																24,000,000	24,000,000
Federal Benefit																$ 18,000,000	$ 18,000,000
Carryforward expiration date range, low							2019
Carryforward expiration date range, high							2037
Plant Related Regulatory Liability [Member]
Federal Tax Reform [Abstract]
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Regulatory Liability, Provisional Income Tax (Expense) Benefit								2,700,000,000
Non-Plant Related Regulated Liability [Member]
Federal Tax Reform [Abstract]
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Regulatory Liability, Provisional Income Tax (Expense) Benefit								174,000,000
Non-Plant Related Regulatory Asset [Member]
Federal Tax Reform [Abstract]
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Regulatory Asset, Provisional Income Tax Expense (Benefit)								$ 254,000,000

[1] Prior periods have been reclassified to conform to current year presentation.

[2] ARAM has been deferred when regulatory treatment has not been established. As Xcel Energy received direction from its regulatory commissions regarding the return of excess deferred taxes to customers, the ARAM deferral was reversed. This resulted in a reduction to tax expense with a corresponding reduction to revenue.

[3] ARAM is a method to flow back excess deferred taxes to customers.

[4] State tax credit carryforwards are net of federal detriment of $24 million as of Dec. 31, 2018 and 2017.

[5] Valuation allowances for state tax credit carryforwards were net of federal benefit of $18 million as of Dec. 31, 2018 and 2017.