Income Taxes (Details) - USD ($)		3 Months Ended				9 Months Ended
		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2015
Income Tax Examination [Line Items]
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards		$ (1,000,000)	$ (1,100,000)
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%		21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		6.20%		6.20%
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	[1]	(0.50%)		(1.80%)
Regulatory difference - reversal of prior quarters' ARAM deferral (b)		(0.80%)		(0.80%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		0.30%		0.10%
Effective Income Tax Rate Reconciliation, Percent		26.20%		24.70%
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions		$ 2,000,000	2,000,000
Unrecognized tax benefit — Temporary tax positions		900,000	800,000
Total unrecognized tax benefit		2,900,000	2,800,000
NOL and tax credit carryforwards		(2,000,000)	(2,100,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible		2,200,000
Amounts accrued for penalties related to unrecognized tax benefits		0	$ 0
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Year(s) under examination			2014-2016			2012 and 2013
Tax years under examination, Concluded					2012 and 2013
Potential Tax Adjustments		0
State Jurisdiction (Wisconsin)
Tax Audits [Abstract]
Year(s) under examination			2014-2016
Potential Tax Adjustments		$ 0
Earliest year subject to examination		2014

[1] Regulatory differences for income tax purposes primarily include the average rate assumption method (ARAM), ARAM deferral and AFUDC - Equity. ARAM is a method to flow back excess deferred taxes to customers. 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.