Income Taxes (Details) - USD ($)		3 Months Ended					12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2015	Dec. 31, 2018
Tax Audits [Abstract]
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		2.10%		2.40%
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	[1]	(4.60%)		(2.70%)
Regulatory differences - reversal of prior quarters' ARAM deferral (b)		(0.60%)		(0.70%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		(0.70%)		0.00%
Effective Income Tax Rate Reconciliation, Percent		17.20%		20.00%
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit - Permanent tax positions		$ 3,100,000	$ 3,000,000				$ 3,000,000
Unrecognized tax benefit - Temporary tax positions		1,600,000	1,500,000				1,500,000
Total unrecognized tax benefit		4,700,000	4,500,000				4,500,000
NOL and tax credit carryforwards		(4,000,000)	(3,800,000)				(3,800,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards		(900,000)	(800,000)				(800,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible		3,600,000
Amounts accrued for penalties related to unrecognized tax benefits		0	0				0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Receivable for interest related to unrecognized tax benefits at beginning of period		700,000		$ 500,000			500,000
Interest income related to unrecognized tax benefits		0					200,000
Receivable for interest related to unrecognized tax benefits at end of period		700,000	$ 700,000				$ 700,000
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
TEXAS
Tax Audits [Abstract]
Earliest year subject to examination		2009

[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.