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, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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								$ 210,000,000
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Net Income Reduction								1,000,000
Unrecognized Tax Benefits [Abstract]
Unrecognized Tax Benefits - Permanent tax positions													$ 2,000,000	$ 1,400,000
Unrecognized tax benefit — Temporary tax positions													800,000	1,000,000
Total unrecognized tax benefit		$ 2,400,000	$ 2,800,000				$ 2,400,000	5,300,000		$ 4,500,000			2,800,000	2,400,000	$ 5,300,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at Jan. 1							2,400,000	5,300,000		4,500,000
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions							200,000	400,000		500,000
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions							(100,000)	(300,000)		0
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions							700,000	1,300,000		500,000
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions							(300,000)	(4,300,000)		(200,000)
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities							(100,000)	0		0
Balance at Dec. 31		$ 2,400,000	$ 2,800,000				$ 2,800,000	$ 2,400,000		$ 5,300,000
Tax Benefits Associated With NOL And Tax Credit Carryforwards [Abstract]
NOL and tax credit carryforwards													(2,100,000)	(1,900,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards													(1,100,000)	(800,000)
Decrease in Unrecognized Tax Benefits is Reasonably Possible													2,200,000
Amounts accrued for penalties related to unrecognized tax benefits													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							6.20%	5.10%	[1]	5.10%	[1]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	[2]						(4.30%)	(0.10%)	[1]	(0.20%)	[1]
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Percent	[3]						4.10%	0.00%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent							(1.30%)	(1.70%)	[1]	(0.60%)	[1]
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items							(0.80%)	(1.00%)	[1]	(0.70%)	[1]
Effective Income Tax Reconciliation, Adjustments Attributable to Tax Returns, Percent							(0.60%)	(2.30%)	[1]	(0.30%)	[1]
Effective Income Tax Rate Reconciliation Change In Unrecognized Tax Benefits, Percent							0.40%	0.80%	[1]	0.10%	[1]
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.00%	0.00%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent							0.10%	0.00%	[1]	(0.10%)	[1]
Effective Income Tax Rate Reconciliation, Percent							24.80%	35.80%	[1]	38.30%	[1]
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)							$ 7,600,000	$ 2,800,000		$ 5,400,000
Current State and Local Tax Expense (Benefit)							1,700,000	0		100,000
Current Change In Unrecognized Tax Expense (Benefit)							200,000	(3,700,000)		500,000
Deferred Federal Income Tax Expense (Benefit)							15,600,000	32,900,000		29,600,000
Deferred State and Local Income Tax Expense (Benefit)							7,400,000	8,000,000		8,200,000
Deferred Change In Unrecognized Tax Expense (Benefit)							300,000	4,700,000		(400,000)
Deferred investment tax credits							(500,000)	(500,000)		(500,000)
Income Tax Expense (Benefit)							32,300,000	44,200,000		42,900,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred tax expense (benefit) excluding selected items							24,000,000	(173,900,000)		39,500,000
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities							(700,000)	219,500,000		(2,100,000)
Deferred Income Tax Expense (Benefit)							$ 23,300,000	45,600,000		$ 37,400,000
Deferred Tax Liabilities, Gross [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment													281,100,000	269,500,000
Deferred Tax Liabilities, Regulatory Assets													55,400,000	58,400,000
Deferred Tax Liabilities, Compensation and Benefits, Employee Benefits													13,900,000	14,200,000
Deferred Tax Liabilities, Other													6,900,000	7,000,000
Deferred Tax Liabilities, Gross													357,300,000	349,100,000
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets Regulatory Liabilities													53,400,000	55,800,000
Deferred Tax Assets, Operating Loss Carryforwards													400,000	12,600,000
Deferred Tax Assets Environmental Remediation													7,800,000	8,100,000
Deferred Tax Assets Tax credit carryforward													4,700,000	4,600,000
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits													4,100,000	3,900,000
Deferred Tax Assets Deferred Investment Tax Credits													3,000,000	3,200,000
Deferred Tax Assets, Other													3,200,000	4,200,000
Deferred Tax Assets, Net of Valuation Allowance													76,600,000	92,400,000
Deferred Tax Liabilities, Net													280,700,000	256,700,000
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Operating Loss Carryforwards													0	57,800,000
Tax Credit Carryforward, Amount													4,700,000	4,300,000
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
WISCONSIN
Tax Audits [Abstract]
Tax years under examination, Concluded				2012 - 2013
Earliest Open Tax Year Subject To Examination							2014
Year(s) under examination			2014 - 2016
Potential Tax Adjustments			$ 0	$ 0
State and Local Jurisdiction
Tax Audits [Abstract]
Operating Loss Carryforwards													$ 2,500,000	$ 5,400,000
Carryforward expiration date range, low							2031
Carryforward expiration date range, high							2033
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								149,000,000
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								41,000,000
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)								$ 23,000,000

[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.