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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, 2015 | Dec. 31, 2014 | Dec. 31, 2013 | 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% |  |  |  |  |  |  |  |  |  |  |  |
Reclassification of deferred taxes to regulatory liabilities, grossed-up for taxes |  |  |  |  |  |  |  | $ 3,800,000,000 |  |  |  |  |  |  |  |  |  |  |
Regulatory liability, customer refunds, weighted average period |  |  |  |  |  |  |  | 30 years |  |  |  |  |  |  |  |  |  |  |
Provisional income tax expense for tax reform |  |  |  |  |  |  |  | $ 23,000,000 |  |  |  |  |  |  |  |  |  |  |
Federal Tax Loss Carryback Claims [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number Of Years Of Tax Loss Carryback Period |  |  |  |  |  |  | two |  |  |  |  |  |  |  |  |  |  |  |
Tax Adjustments, Settlements, and Unusual Provisions |  |  |  |  |  |  |  |  |  |  |  | $ 5,000,000 | $ 17,000,000 | $ 12,000,000 | $ 15,000,000 |  |  |  |
Tax Audits [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized Tax Benefits, Interest on Income Taxes Accrued |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ (3,000,000) | $ 0
Unrecognized Tax Benefits, Interest on Income Taxes Accrued |  |  |  |  |  |  | $ 0 | (3,000,000) |  | $ 3,000,000 |  |  |  |  |  |  |  |  |
Unrecognized Tax Benefits [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized tax benefit — Permanent tax positions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 28,000,000 | 20,000,000 |  |
Unrecognized tax benefit — Temporary tax positions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,000,000 | 19,000,000 |  |
Total unrecognized tax benefit |  | $ 39,000,000 | $ 37,000,000 |  |  |  | 39,000,000 | 134,000,000 |  | 121,000,000 |  | 121,000,000 |  |  |  | 37,000,000 | 39,000,000 | 134,000,000 | $ 121,000,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balance at Jan. 1 |  |  |  |  |  |  | 39,000,000 | 134,000,000 |  | 121,000,000 |  |  |  |  |  |  |  |  |
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions |  |  |  |  |  |  | 9,000,000 | 6,000,000 |  | 8,000,000 |  |  |  |  |  |  |  |  |
Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions |  |  |  |  |  |  | (4,000,000) | (4,000,000) |  | 0 |  |  |  |  |  |  |  |  |
Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions |  |  |  |  |  |  | 2,000,000 | 15,000,000 |  | 10,000,000 |  |  |  |  |  |  |  |  |
Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions |  |  |  |  |  |  | (4,000,000) | (105,000,000) |  | (5,000,000) |  |  |  |  |  |  |  |  |
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities |  |  |  |  |  |  | (5,000,000) | (7,000,000) |  | 0 |  |  |  |  |  |  |  |  |
Balance at Dec. 31 |  | $ 39,000,000 | $ 37,000,000 |  |  |  | $ 37,000,000 | $ 39,000,000 |  | $ 134,000,000 |  | $ 121,000,000 |  |  |  |  |  |  |
Tax Benefits Associated With NOL And Tax Credit Carryforwards [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
NOL and tax credit carryforwards |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (35,000,000) | (31,000,000) |  |
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (24,000,000) | (13,000,000) |  |
Upper bound of decrease in unrecognized tax benefit that is reasonably possible |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 28,000,000 |  |  |
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 |  |  |  |  |  |  | 5.00% | 4.10% | [1] | 4.10% | [1] |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, Tax Credit, Percent |  |  |  |  |  |  | (5.20%) | (4.70%) | [1] | (3.40%) | [1] |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation Regulatory Differences Utility Plant Items, Percent |  |  |  |  |  |  | (2.00%) | (1.00%) | [1] | (0.80%) | [1] |  |  |  |  |  |  |  |
Tax reform, Percent | [2] |  |  |  |  |  | 0.60% | 0.00% | [1] | 0.00% | [1] |  |  |  |  |  |  |  |
Regulatory differences - effects of rate changes, Percent | [3] |  |  |  |  |  | (5.80%) | (0.10%) | [1] | (0.10%) | [1] |  |  |  |  |  |  |  |
Regulatory differences - other utility plant items, Percent |  |  |  |  |  |  | (1.00%) | (0.70%) | [1] | (0.50%) | [1] |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation Change In Unrecognized Tax Benefits, Percent |  |  |  |  |  |  | 0.40% | (0.60%) | [1] | 0.20% | [1] |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent |  |  |  |  |  |  | 0.00% | 1.40% | [1] | 0.00% | [1] |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent |  |  |  |  |  |  | (0.40%) | (1.30%) | [1] | (0.40%) | [1] |  |  |  |  |  |  |  |
Effective Income Tax Rate Reconciliation, Percent |  |  |  |  |  |  | 12.60% | 32.10% | [1] | 34.10% | [1] |  |  |  |  |  |  |  |
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current Federal Tax Expense (Benefit) |  |  |  |  |  |  | $ (34,000,000) | $ 1,000,000 |  | $ (3,000,000) |  |  |  |  |  |  |  |  |
Current State and Local Tax Expense (Benefit) |  |  |  |  |  |  | 8,000,000 | (11,000,000) |  | (4,000,000) |  |  |  |  |  |  |  |  |
Current Change In Unrecognized Tax Expense (Benefit) |  |  |  |  |  |  | (6,000,000) | (83,000,000) |  | 6,000,000 |  |  |  |  |  |  |  |  |
Deferred Federal Income Tax Expense (Benefit) |  |  |  |  |  |  | 122,000,000 | 460,000,000 |  | 477,000,000 |  |  |  |  |  |  |  |  |
Deferred State and Local Income Tax Expense (Benefit) |  |  |  |  |  |  | 85,000,000 | 107,000,000 |  | 112,000,000 |  |  |  |  |  |  |  |  |
Deferred Change In Unrecognized Tax Expense (Benefit) |  |  |  |  |  |  | 11,000,000 | 73,000,000 |  | (2,000,000) |  |  |  |  |  |  |  |  |
Deferred investment tax credits |  |  |  |  |  |  | (5,000,000) | (5,000,000) |  | (5,000,000) |  |  |  |  |  |  |  |  |
Income Tax Expense (Benefit) |  |  |  |  |  |  | 181,000,000 | 542,000,000 |  | 581,000,000 |  |  |  |  |  |  |  |  |
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred tax expense (benefit) excluding selected items |  |  |  |  |  |  | 320,000,000 | (2,939,000,000) |  | 631,000,000 |  |  |  |  |  |  |  |  |
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities |  |  |  |  |  |  | (102,000,000) | 3,583,000,000 |  | (45,000,000) |  |  |  |  |  |  |  |  |
Other Comprehensive Income (Loss), Tax |  |  |  |  |  |  | 0 | (4,000,000) |  | 1,000,000 |  |  |  |  |  |  |  |  |
Deferred Income Tax Expense (Benefit) |  |  |  |  |  |  | $ 218,000,000 | 640,000,000 |  | $ 587,000,000 |  |  |  |  |  |  |  |  |
Deferred Tax Liabilities, Gross [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Tax Liabilities, Property, Plant and Equipment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,082,000,000 | 4,960,000,000 |  |
Deferred Tax Liabilities, Regulatory Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 599,000,000 | 565,000,000 |  |
Pension expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 178,000,000 | 199,000,000 |  |
Deferred Tax Liabilities, Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 64,000,000 | 57,000,000 |  |
Deferred Tax Liabilities, Gross |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,923,000,000 | 5,781,000,000 |  |
Deferred Tax Assets, Gross [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred Tax Assets Regulatory Liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 879,000,000 | 886,000,000 |  |
Deferred Tax Assets Tax credit carryforward |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 642,000,000 | 607,000,000 |  |
Deferred Tax Assets, Operating Loss Carryforwards |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 51,000,000 | 293,000,000 |  |
Deferred Tax Assets, Valuation Allowance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (79,000,000) | (77,000,000) |  |
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 124,000,000 | 132,000,000 |  |
Deferred Tax Assets Deferred Investment Tax Credits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16,000,000 | 17,000,000 |  |
Deferred Tax Assets Rate Refund |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 60,000,000 | 10,000,000 |  |
Deferred Tax Assets, Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 65,000,000 | 68,000,000 |  |
Deferred Tax Assets, Net of Valuation Allowance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,758,000,000 | 1,936,000,000 |  |
Deferred Tax Liabilities, Net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,165,000,000 | 3,845,000,000 |  |
Internal Revenue Service (IRS) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Audits [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Loss Carryforwards |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 1,072,000,000 |  |
Tax Credit Carryforward, Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 553,000,000 | 517,000,000 |  |
Tax Credit Carryforward, Valuation Allowance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (5,000,000) | (5,000,000) |  |
Carryforward expiration date range, low |  |  |  |  |  |  | 2021 |  |  |  |  |  |  |  |  |  |  |  |
Carryforward expiration date range, high |  |  |  |  |  |  | 2038 |  |  |  |  |  |  |  |  |  |  |  |
Tax years under examination, Concluded |  |  |  |  | 2012 and 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax years 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 |  |  |  |  |  |  |  |  |  |  |  |
Minnesota |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Audits [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax years under examination, Concluded |  |  | 2010 - 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Earliest year subject to examination |  |  |  |  |  |  | 2009 |  |  |  |  |  |  |  |  |  |  |  |
Potential Tax Adjustments |  |  |  | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Texas |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Audits [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Earliest year subject to examination |  |  |  |  |  |  | 2010 |  |  |  |  |  |  |  |  |  |  |  |
Wisconsin |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Audits [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax years under examination, Concluded |  |  |  | 2012 - 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Earliest year subject to examination |  |  |  |  |  |  | 2014 |  |  |  |  |  |  |  |  |  |  |  |
Tax years under examination |  |  | 2014 - 2016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential Tax Adjustments |  |  | $ 0 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
State and Local Jurisdiction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Tax Audits [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Loss Carryforwards |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,104,000,000 | 1,592,000,000 |  |
Operating Loss Carryforwards, Valuation Allowance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (50,000,000) | (55,000,000) |  |
Tax Credit Carryforward Net Of Federal Detriment | [4] |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 89,000,000 | 90,000,000 |  |
Valuation Allowance for Tax Credit Carryforward Net of Federal Benefit | [5] |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (69,000,000) | (68,000,000) |  |
Federal detriment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 24,000,000 | 24,000,000 |  |
Federal Benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18,000,000 | $ 18,000,000 |  |
Carryforward expiration date range, low |  |  |  |  |  |  | 2019 |  |  |  |  |  |  |  |  |  |  |  |
Carryforward expiration date range, high |  |  |  |  |  |  | 2037 |  |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  | 2,700,000,000 |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  | 174,000,000 |  |  |  |  |  |  |  |  |  |  |
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) |  |  |  |  |  |  |  | $ 254,000,000 |  |  |  |  |  |  |  |  |  |  |
[1] | Prior periods have been reclassified to conform to current year presentation.
[2] | 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.
[3] | ARAM is a method to flow back excess deferred taxes to customers.
[4] | State tax credit carryforwards are net of federal detriment of $24 million as of Dec. 31, 2018 and 2017.
[5] | Valuation allowances for state tax credit carryforwards were net of federal benefit of $18 million as of Dec. 31, 2018 and 2017.

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