Income Taxes (Details) - USD ($)		1 Months Ended	3 Months Ended			12 Months Ended
		Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2017	Sep. 30, 2015	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		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%
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Regulatory Liability, Provisional Income Tax (Expense) Benefit, Gross							$ 559,000,000
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)							8,000,000
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Net Income Reduction							2,000,000
Tax Audits [Abstract]
Unrecognized Tax Benefits, Interest on Income Taxes Accrued												$ (700,000)	$ (500,000)	$ (900,000)	$ 0
Interest Income (Expense) related to unrecognized tax benefits						$ (200,000)	(1,400,000)		$ 900,000
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions												3,000,000	2,300,000
Unrecognized tax benefit — Temporary tax positions												1,500,000	2,000,000
Total unrecognized tax benefit		$ 4,300,000	$ 4,500,000			4,300,000	28,700,000		24,700,000			4,500,000	4,300,000	28,700,000	$ 24,700,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at Jan. 1						4,300,000	28,700,000		24,700,000
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions						600,000	900,000		1,400,000
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions						(100,000)	(600,000)		0
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions						100,000	1,300,000		3,900,000
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions						(300,000)	(19,900,000)		(1,300,000)
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						(100,000)	(6,100,000)		0
Balance at Dec. 31		$ 4,300,000	$ 4,500,000			$ 4,500,000	$ 4,300,000		$ 28,700,000
Tax Benefits Associated With NOL And Tax Credit Carryforwards [Abstract]
NOL and tax credit carryforwards												(3,800,000)	(5,900,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards												(800,000)	(2,700,000)
Decrease in Unrecognized Tax Benefits is Reasonably Possible												3,600,000
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						2.30%	2.00%	[1]	2.20%	[1]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	[2]					(4.20%)	0.00%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent						0.00%	(3.50%)	[1]	0.00%	[1]
Effective Income Tax Reconciliation, Adjustments Attributable to Tax Returns, Percent						(1.50%)	(0.40%)	[1]	(1.10%)	[1]
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent						(1.30%)	(0.80%)	[1]	(1.00%)	[1]
Amortization of excess nonplant deferred taxes						(1.20%)	(0.00%)	[1]	(0.00%)	[1]
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items						(0.70%)	(0.70%)	[1]	(0.50%)	[1]
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Percent	[3]					0.70%	0.00%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation Change In Unrecognized Tax Benefits						0.10%	(1.00%)	[1]	0.80%	[1]
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent						0.20%	(0.50%)	[1]	(0.40%)	[1]
Effective Income Tax Rate Reconciliation, Percent						15.40%	30.10%	[1]	35.00%	[1]
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)						$ 12,300,000	$ (20,900,000)		$ (40,900,000)
Current State and Local Tax Expense (Benefit)						2,300,000	(12,800,000)		(2,900,000)
Current Change In Unrecognized Tax Expense (Benefit)						2,300,000	(24,300,000)		3,100,000
Deferred Federal Income Tax Expense (Benefit)						20,500,000	89,900,000		116,400,000
Deferred State and Local Income Tax Expense (Benefit)						3,600,000	14,500,000		7,800,000
Deferred Change In Unrecognized Tax Expense (Benefit)						(2,000,000)	22,100,000		(1,200,000)
Deferred investment tax credits						(100,000)	(100,000)		(200,000)
Income Tax Expense (Benefit)						38,900,000	68,400,000		82,100,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred tax expense (benefit) excluding selected items						44,200,000	(414,200,000)		128,400,000
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities						(22,000,000)	540,700,000		(5,400,000)
Other Comprehensive Income (Loss), Tax						(100,000)	0		0
Deferred Income Tax Expense (Benefit)						$ 22,100,000	126,500,000		$ 123,000,000
Deferred Tax Liabilities, Gross [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment												680,600,000	654,400,000
Deferred Tax Liabilities, Regulatory Assets												49,200,000	46,800,000
Deferred Tax Liabilities, Compensation and Benefits, Employee Benefits												32,300,000	33,800,000
Deferred Tax Liabilities, Other												2,900,000	4,600,000
Deferred Tax Liabilities, Gross												765,000,000	739,600,000
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets Regulatory Liabilities												116,800,000	114,600,000
Deferred Tax Assets, Operating Loss Carryforwards												200,000	26,200,000
Deferred Tax Assets Unbilled Revenue Fuel Costs												12,700,000	10,400,000
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits												5,600,000	5,800,000
Deferred Tax Assets, Tax Credit Carryforwards												5,700,000	5,200,000
Deferred Tax Assets, Other												4,900,000	2,500,000
Deferred Tax Assets, Net of Valuation Allowance												145,900,000	164,700,000
Deferred Tax Liabilities, Net												619,100,000	574,900,000
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Operating Loss Carryforwards												0	115,000,000
Tax Credit Carryforward, Amount												5,700,000	5,200,000
Carryforward expiration date range, low						2021
Carryforward expiration date range, high						2038
Tax years under examination, Concluded				2012 and 2013
Year(s) under examination			2014 - 2016		2012 and 2013						2010 and 2011
Year of carryback claim under examination											2009
Potential Tax Adjustments			$ 0
TEXAS
Tax Audits [Abstract]
Earliest year subject to examination						2010
State and Local Jurisdiction
Tax Audits [Abstract]
Operating Loss Carryforwards												$ 2,900,000	$ 40,500,000
Carryforward expiration date range, low						2021
Carryforward expiration date range, high						2036
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							426,000,000
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							28,000,000
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)							$ 45,000,000

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

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

[3] 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.