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							$ 1,500,000,000
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)							18,000,000
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Net Income Reduction							4,000,000
Tax Audits [Abstract]
Unrecognized Tax Benefits, Interest on Income Taxes Accrued												$ (700,000)	$ (300,000)	$ (1,100,000)	$ (400,000)
Interest Income (Expense) related to unrecognized tax benefits						$ 400,000	(800,000)		$ 700,000
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions												5,400,000	4,000,000
Unrecognized tax benefit — Temporary tax positions												4,900,000	6,100,000
Total unrecognized tax benefit		$ 10,100,000	$ 10,300,000			10,100,000	19,700,000		17,400,000			10,300,000	10,100,000	19,700,000	$ 17,400,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at Jan. 1						10,100,000	19,700,000		17,400,000
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions						1,100,000	1,900,000		2,700,000
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions						(300,000)	(1,500,000)		0
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions						400,000	4,400,000		500,000
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions						(100,000)	(14,400,000)		(900,000)
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities						(900,000)	0		0
Balance at Dec. 31		$ 10,100,000	$ 10,300,000			$ 10,300,000	$ 10,100,000		$ 19,700,000
Tax Benefits Associated With Nol And Tax Credit Carryforwards [Abstract]
NOL and tax credit carryforwards												(5,600,000)	(4,000,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards												(2,000,000)	300,000
Upper bound of decrease in unrecognized tax benefit that is reasonably possible												8,700,000
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						3.70%	3.00%	[1]	3.00%	[1]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	[2]					(3.00%)	(0.10%)	[1]	(0.10%)	[1]
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent						(1.70%)	(0.90%)	[1]	(0.50%)	[1]
Amortization of excess nonplant deferred taxes						(1.40%)	(0.00%)	[1]	(0.00%)	[1]
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items						(0.90%)	(0.90%)	[1]	(0.70%)	[1]
Effective Income Tax Rate Reconciliation, Tax Credit, Percent						(0.60%)	(0.00%)	[1]	(0.00%)	[1]
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Percent	[3]					0.20%	0.00%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation Change In Unrecognized Tax Benefits, Percent						0.10%	0.20%	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent						0.00%	(2.40%)	[1]	0.00%	[1]
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent						(0.30%)	(0.10%)	[1]	0.40%	[1]
Effective Income Tax Rate Reconciliation, Percent						17.10%	33.80%	[1]	37.10%	[1]
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)						$ 79,500,000	$ 40,400,000		$ 45,300,000
Current State and Local Tax Expense (Benefit)						14,200,000	14,600,000		8,700,000
Current Change In Unrecognized Tax Expense (Benefit)						(1,300,000)	(7,800,000)		700,000
Deferred Federal Income Tax Expense (Benefit)						4,900,000	176,400,000		195,100,000
Deferred State and Local Income Tax Expense (Benefit)						16,600,000	22,500,000		27,200,000
Deferred Change In Unrecognized Tax Expense (Benefit)						2,300,000	8,900,000		(300,000)
Deferred investment tax credits						(2,500,000)	(2,800,000)		(2,800,000)
Income Tax Expense (Benefit)						113,700,000	252,200,000		273,900,000
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred tax expense (benefit) excluding selected items						74,800,000	(1,244,700,000)		230,900,000
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities						(50,600,000)	1,453,100,000		(8,400,000)
Other Comprehensive Income (Loss), Tax						(400,000)	(600,000)		(500,000)
Deferred Income Tax Expense (Benefit)						$ 23,800,000	207,800,000		$ 222,000,000
Deferred Tax Liabilities, Gross [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment												1,860,100,000	1,790,100,000
Deferred Tax Liabilities, Regulatory Assets												251,100,000	252,400,000
Deferred Tax Liabilities, Compensation and Benefits, Employee Benefits												33,900,000	60,000,000
Deferred Tax Liabilities, Other												13,100,000	3,700,000
Deferred Tax Liabilities, Gross												2,158,200,000	2,106,200,000
Deferred Tax Assets, Gross [Abstract]
Deferred Tax Assets Regulatory Liabilities												336,300,000	338,000,000
Deferred Tax Assets, Operating Loss Carryforwards												18,200,000	39,300,000
Deferred Tax Assets Tax credit carryforward												51,900,000	39,300,000
Deferred Tax Assets, Valuation Allowance												(8,900,000)	0
Deferred Tax Assets Deferred Investment Tax Credits												6,300,000	6,900,000
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits												2,800,000	6,800,000
Deferred Tax Assets Rate Refund												9,300,000	900,000
Deferred Tax Assets, Other												23,000,000	30,500,000
Deferred Tax Assets, Net of Valuation Allowance												438,900,000	461,700,000
Deferred Tax Liabilities, Net												1,719,300,000	1,644,500,000
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Operating Loss Carryforwards												0	67,600,000
Tax Credit Carryforward, Amount												35,000,000	29,800,000
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
COLORADO
Tax Audits [Abstract]
Earliest year subject to examination						2009
State and Local Jurisdiction
Tax Audits [Abstract]
Operating Loss Carryforwards												484,700,000	679,200,000
Tax Credit Carryforward Net Of Federal Detriment	[4]											16,900,000	16,800,000
Valuation Allowance for Tax Credit Carryforward Net of Federal Benefit	[5]											(8,900,000)	(7,300,000)
Federal detriment												4,500,000	4,500,000
Federal Benefit												$ 2,400,000	$ 1,900,000
Carryforward expiration date range, low						2019
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							1,100,000,000
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							50,000,000
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)							$ 54,000,000

[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.

[4] State tax credit carryforwards are net of federal detriment of $4.5 million as of Dec. 31, 2018 and 2017.

[5] Valuation allowances for state tax credit carryforwards were net of federal benefit of $2.4 million and $1.9 million as of Dec. 31, 2018 and 2017, respectively.