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Fair Value of Financial Assets and Liabilities (Tables) | 12 Months Ended
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Dec. 31, 2018
Fair Value Disclosures [Abstract] |
Cost and Fair Value of Nuclear Decommissioning Fund Investments | Non-derivative instruments with recurring fair value measurements in the nuclear decommissioning fund:
|  | Dec. 31, 2018
|  |  |  | Fair Value
(Millions of Dollars) |  | Cost |  | Level 1 |  | Level 2 |  | Level 3 |  | NAV |  | Total
Nuclear decommissioning fund (a) |  |  |  |  |  |  |  |  |  |  |  |
Cash equivalents |  | $ | 24 |  |  | $ | 24 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 24 |
Commingled funds |  | 758 |  |  | 79 |  |  | — |  |  | — |  |  | 819 |  |  | 898 |
Debt securities |  | 466 |  |  | — |  |  | 436 |  |  | — |  |  | — |  |  | 436 |
Equity securities |  | 401 |  |  | 697 |  |  | — |  |  | — |  |  | — |  |  | 697 |
Total |  | $ | 1,649 |  |  | $ | 800 |  |  | $ | 436 |  |  | $ | — |  |  | $ | 819 |  |  | $ | 2,055 |
(a) | Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $141 million of equity investments in unconsolidated subsidiaries and $121 million of rabbi trust assets and miscellaneous investments.
|  | Dec. 31, 2017
|  |  |  | Fair Value
(Millions of Dollars) |  | Cost |  | Level 1 |  | Level 2 |  | Level 3 |  | NAV |  | Total
Nuclear decommissioning fund (a) |  |  |  |  |  |  |  |  |  |  |  |
Cash equivalents |  | $ | 29 |  |  | $ | 29 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 29 |
Commingled funds |  | 701 |  |  | 223 |  |  | — |  |  | — |  |  | 659 |  |  | 882 |
Debt securities |  | 438 |  |  | — |  |  | 441 |  |  | — |  |  | — |  |  | 441 |
Equity securities |  | 423 |  |  | 791 |  |  | — |  |  | — |  |  | — |  |  | 791 |
Total |  | $ | 1,591 |  |  | $ | 1,043 |  |  | $ | 441 |  |  | $ | — |  |  | $ | 659 |  |  | $ | 2,143 |
(a) | Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet, which also includes $140 million of equity investments in unconsolidated subsidiaries and $114 million of rabbi trust assets and miscellaneous investments.
For th
Final Contractual Maturity Dates of Debt Securities in the Nuclear Decommissioning Fund by Asset Class | Contractual maturity dates of debt securities in the nuclear decommissioning fund as of Dec. 31, 2018:
|  | Final Contractual Maturity
(Millions of Dollars) |  | Due in 1 Year or Less |  | Due in 1 to 5 Years |  | Due in 5 to 10 Years |  | Due after 10 Years |  | Total
Debt securities |  | $ | 10 |  |  | $ | 107 |  |  | $ | 211 |  |  | $ | 108 |  |  | $ | 436 |
Rabbi
Rabbi Trust Securities Amortized Cost and Fair Value Measured on Recurrring Basis [Table Text Block] | rusts Xcel Energy has established rabbi trusts to provide partial funding for future distributions of its SERP and deferred compensation plan. Cost and fair value of assets held in rabbi trusts:
|  | Dec. 31, 2018
|  |  |  | Fair Value
(Millions of Dollars) |  | Cost |  | Level 1 |  | Level 2 |  | Level 3 |  | Total
Rabbi Trusts (a) |  |  |  |  |  |  |  |  |  |
Cash equivalents |  | $ | 16 |  |  | $ | 16 |  |  | $ | — |  |  | $ | — |  |  | $ | 16 |
Mutual funds |  | 52 |  |  | 51 |  |  | — |  |  | — |  |  | 51 |
Total |  | $ | 68 |  |  | $ | 67 |  |  | $ | — |  |  | $ | — |  |  | $ | 67 |
|  | Dec. 31, 2017
|  |  |  | Fair Value
(Millions of Dollars) |  | Cost |  | Level 1 |  | Level 2 |  | Level 3 |  | Total
Rabbi Trusts (a) |  |  |  |  |  |  |  |  |  |
Cash equivalents |  | $ | 12 |  |  | $ | 12 |  |  | $ | — |  |  | $ | — |  |  | $ | 12 |
Mutual funds |  | 47 |  |  | 50 |  |  | — |  |  | — |  |  | 50 |
Total |  | $ | 59 |  |  | $ | 62 |  |  | $ | — |  |  | $ | — |  |  | $ | 62 |
(a) | Reported in nuclear decommissioning fund and other investments on the consolidated balance sheet.
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] | Gross notional amounts of commodity forwards, options and FTRs as of Dec. 31:
(Amounts in Millions) (a) (b) |  | 2018 |  | 2017
MWh of electricity |  | 87 |  |  | 68 |
MMBtu of natural gas |  | 92 |  |  | 37 |
(a) | Amounts are not reflective of net positions in the underlying commodities.
(b) | Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.
Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) [Table Text Block] | Financial impact of qualifying interest rate and vehicle fuel cash flow hedges on Xcel Energy’s accumulated other comprehensive loss, included in the consolidated statements of common stockholders’ equity and in the consolidated statements of comprehensive income:
(Millions of Dollars) |  | 2018 |  | 2017 |  | 2016
Accumulated other comprehensive loss related to cash flow hedges at Jan. 1 |  | $ | (58 | ) |  | $ | (51 | ) |  | $ | (55 | )
After-tax net unrealized losses related to derivatives accounted for as hedges |  | (5 | ) |  | — |  |  | — |
After-tax net realized losses on derivative transactions reclassified into earnings |  | 3 |  |  | 3 |  |  | 4 |
Adoption of ASU. 2018-02 (a) |  | — |  |  | (10 | ) |  | — |
Accumulated other comprehensive loss related to cash flow hedges at Dec. 31 |  | $ | (60 | ) |  | $ | (58 | ) |  | $ | (51 | )
(a) | In 2017, Xcel Energy implemented ASU No. 2018-02 related to TCJA, which resulted in reclassification of certain credit balances within net accumulated other comprehensive loss to retained earnings.
Derivative Instruments, Gain (Loss) [Table Text Block] | Impact of derivative activity:
|  | Pre-Tax Fair Value Gains (Losses) Recognized During the Period in:
(Millions of Dollars) |  | Accumulated Other Comprehensive Loss |  | Regulatory (Assets) and Liabilities
Year Ended Dec. 31, 2018 |  |  |  |
Derivatives designated as cash flow hedges |  |  |  |
Interest rate |  | $ | (7 | ) |  | $ | — |
Total |  | $ | (7 | ) |  | $ | — |
Other derivative instruments |  |  |  |
Electric commodity |  | $ | — |  |  | $ | 1 |
Natural gas commodity |  | — |  |  | 10 |
Total |  | $ | — |  |  | $ | 11 |
Year Ended Dec. 31, 2017 |  |  |  |
Other derivative instruments |  |  |  |
Electric commodity |  | $ | — |  |  | $ | 10 |
Natural gas commodity |  | — |  |  | (13 | )
Total |  | $ | — |  |  | $ | (3 | )
Year Ended Dec. 31, 2016 |  |  |  |
Other derivative instruments |  |  |  |
Electric commodity |  | $ | — |  |  | $ | 17 |
Natural gas commodity |  | — |  |  | 1 |
Total |  | $ | — |  |  | $ | 18 |
| Pre-Tax (Gains) Losses Reclassified into Income During the Period from: |  | Pre-Tax Gains (Losses) Recognized During the Period in Income |
(Millions of Dollars) | Accumulated Other Comprehensive Loss |  | Regulatory Assets and (Liabilities) |  |
Year Ended Dec. 31, 2018 |  |  |  |  |  |
Derivatives designated as cash flow hedges |  |  |  |  |  |
Interest rate | $ | 4 |  | (a) | $ | — |  |  | $ | — |  |
Total | $ | 4 |  |  | $ | — |  |  | $ | — |  |
Other derivative instruments |  |  |  |  |  |
Commodity trading | $ | — |  |  | $ | — |  |  | $ | 14 |  | (b)
Electric commodity | — |  |  | (1 | ) | (c) | — |  |
Natural gas commodity | — |  |  | (6 | ) | (d) | (4 | ) | (d)
Total | $ | — |  |  | $ | (7 | ) |  | $ | 10 |  |
Year Ended Dec. 31, 2017 |  |  |  |  |  |
Derivatives designated as cash flow hedges |  |  |  |  |  |
Interest rate | $ | 5 |  | (a) | $ | — |  |  | $ | — |  |
Total | $ | 5 |  |  | $ | — |  |  | $ | — |  |
Other derivative instruments |  |  |  |  |  |
Commodity trading | $ | — |  |  | $ | — |  |  | $ | 10 |  | (b)
Electric commodity | — |  |  | (15 | ) | (c) | — |  |
Natural gas commodity | — |  |  | 3 |  | (d) | (6 | ) | (d)
Total | $ | — |  |  | $ | (12 | ) |  | $ | 4 |  |
Year Ended Dec. 31, 2016 |  |  |  |  |  |
Derivatives designated as cash flow hedges |  |  |  |  |  |
Interest rate | $ | 6 |  | (a) | $ | — |  |  | $ | — |  |
Total | $ | 6 |  |  | $ | — |  |  | $ | — |  |
Other derivative instruments |  |  |  |  |  |
Commodity trading | $ | — |  |  | $ | — |  |  | $ | 2 |  | (b)
Electric commodity | — |  |  | (8 | ) | (c) | — |  |
Natural gas commodity | — |  |  | 15 |  | (d) | (8 | ) | (d)
Total | $ | — |  |  | $ | 7 |  |  | $ | (6 | ) |
(a) | Amounts recorded to interest charges.
(b) | Amounts recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue, as appropriate.
(c) | Amounts recorded to electric fuel and purchased power. These derivative settlement gains and losses are shared with electric customers through fuel and purchased energy cost-recovery mechanisms, and reclassified out of income as regulatory assets or liabilities, as appropriate.
(d) | Amounts for the year ended Dec. 31, 2018 included $1 million of settlement losses on derivatives entered to mitigate natural gas price risk for electric generation recorded to electric fuel and purchased power, subject to cost-recovery mechanisms and reclassified to a regulatory asset, as appropriate. Such gains and losses for the years ended Dec. 31, 2017 and 2016 were immaterial. Remaining settlement losses for the years ended Dec. 31, 2018, 2017 and 2016 related to natural gas operations and were recorded to cost of natural gas sold and transported. These losses are subject to cost-recovery mechanisms and reclassified out of income to a regulatory asset, as appropriate.
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] | Xcel Energy’s derivative assets and liabilities measured at fair value on a recurring basis:
|  | Dec. 31, 2018 |  | Dec. 31, 2017
|  | Fair Value |  | Fair Value Total |  | Netting (a) |  |  |  | Fair Value |  | Fair Value Total |  | Netting (a) |  |
(Millions of Dollars) |  | Level 1 |  | Level 2 |  | Level 3 |  |  |  | Total |  | Level 1 |  | Level 2 |  | Level 3 |  |  |  | Total
Current derivative assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity trading |  | $ | 4 |  |  | $ | 92 |  |  | $ | 2 |  |  | $ | 98 |  |  | $ | (44 | ) |  | $ | 54 |  |  | $ | 2 |  |  | $ | 22 |  |  | $ | — |  |  | $ | 24 |  |  | $ | (15 | ) |  | $ | 9 |
Electric commodity |  | — |  |  | — |  |  | 25 |  |  | 25 |  |  | — |  |  | 25 |  |  | — |  |  | — |  |  | 32 |  |  | 32 |  |  | (2 | ) |  | 30 |
Natural gas commodity |  | — |  |  | 4 |  |  | — |  |  | 4 |  |  | — |  |  | 4 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Total current derivative assets |  | $ | 4 |  |  | $ | 96 |  |  | $ | 27 |  |  | $ | 127 |  |  | $ | (44 | ) |  | 83 |  |  | $ | 2 |  |  | $ | 22 |  |  | $ | 32 |  |  | $ | 56 |  |  | $ | (17 | ) |  | 39 |
PPAs (b) |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |  |  | 5 |
Current derivative instruments |  |  |  |  |  |  |  |  |  |  |  | $ | 87 |  |  |  |  |  |  |  |  |  |  |  |  | $ | 44 |
Noncurrent derivative assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other derivative instruments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity trading |  | $ | — |  |  | $ | 27 |  |  | $ | 5 |  |  | $ | 32 |  |  | $ | (14 | ) |  | $ | 18 |  |  | $ | — |  |  | $ | 31 |  |  | $ | 5 |  |  | $ | 36 |  |  | $ | (7 | ) |  | $ | 29 |
Total noncurrent derivative assets |  | $ | — |  |  | $ | 27 |  |  | $ | 5 |  |  | $ | 32 |  |  | $ | (14 | ) |  | 18 |  |  | $ | — |  |  | $ | 31 |  |  | $ | 5 |  |  | $ | 36 |  |  | $ | (7 | ) |  | 29 |
PPAs (b) |  |  |  |  |  |  |  |  |  |  |  | 16 |  |  |  |  |  |  |  |  |  |  |  |  | 19 |
Noncurrent derivative instruments |  |  |  |  |  |  |  |  |  |  |  | $ | 34 |  |  |  |  |  |  |  |  |  |  |  |  | $ | 48 |
|  | Dec. 31, 2018 |  | Dec. 31, 2017
|  | Fair Value |  | Fair Value Total |  | Netting (a) |  |  |  | Fair Value |  | Fair Value Total |  | Netting (a) |  |
(Millions of Dollars) |  | Level 1 |  | Level 2 |  | Level 3 |  |  |  | Total |  | Level 1 |  | Level 2 |  | Level 3 |  |  |  | Total
Current derivative liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives designated as cash flow hedges: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  | $ | — |  |  | $ | 7 |  |  | $ | — |  |  | $ | 7 |  |  | $ | — |  |  | $ | 7 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Other derivative instruments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity trading |  | 4 |  |  | 88 |  |  | 2 |  |  | 94 |  |  | (60 | ) |  | 34 |  |  | 2 |  |  | 18 |  |  | — |  |  | 20 |  |  | (15 | ) |  | 5 |
Electric commodity |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 2 |  |  | 2 |  |  | (2 | ) |  | — |
Natural gas commodity |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 1 |  |  | — |  |  | 1 |  |  | — |  |  | 1 |
Total current derivative liabilities |  | $ | 4 |  |  | $ | 95 |  |  | $ | 2 |  |  | $ | 101 |  |  | $ | (60 | ) |  | 41 |  |  | $ | 2 |  |  | $ | 19 |  |  | $ | 2 |  |  | $ | 23 |  |  | $ | (17 | ) |  | 6 |
PPAs (b) |  |  |  |  |  |  |  |  |  |  |  | 20 |  |  |  |  |  |  |  |  |  |  |  |  | 23 |
Current derivative instruments |  |  |  |  |  |  |  |  |  |  |  | $ | 61 |  |  |  |  |  |  |  |  |  |  |  |  | $ | 29 |
Noncurrent derivative liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other derivative instruments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity trading |  | $ | — |  |  | $ | 18 |  |  | $ | 1 |  |  | $ | 19 |  |  | $ | 17 |  |  | $ | 36 |  |  | $ | — |  |  | $ | 24 |  |  | $ | — |  |  | $ | 24 |  |  | $ | (10 | ) |  | $ | 14 |
Total noncurrent derivative liabilities |  | $ | — |  |  | $ | 18 |  |  | $ | 1 |  |  | $ | 19 |  |  | $ | 17 |  |  | 36 |  |  | $ | — |  |  | $ | 24 |  |  | $ | — |  |  | $ | 24 |  |  | $ | (10 | ) |  | 14 |
PPAs (b) |  |  |  |  |  |  |  |  |  |  |  | 93 |  |  |  |  |  |  |  |  |  |  |  |  | 112 |
Noncurrent derivative instruments |  |  |  |  |  |  |  |  |  |  |  | $ | 129 |  |  |  |  |  |  |  |  |  |  |  |  | $ | 126 |
(a) | Xcel Energy nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements as of Dec. 31, 2018 and 2017. At Dec. 31, 2018 and 2017, derivative assets and liabilities include $32 million and $0 million of obligations to return cash collateral, respectively. At Dec. 31, 2018 and 2017, derivative assets and liabilities include rights to reclaim cash collateral of $15 million and $3 million, respectively. Counterparty netting excludes settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
(b) | During 2006, Xcel Energy qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Table Text Block] | Changes in Level 3 commodity derivatives:
|  | Year Ended Dec. 31
(Millions of Dollars) |  | 2018 |  | 2017 |  | 2016
Balance at Jan. 1 |  | $ | 35 |  |  | $ | 17 |  |  | $ | 18 |
Purchases |  | 59 |  |  | 82 |  |  | 35 |
Settlements |  | (59 | ) |  | (97 | ) |  | (89 | )
Net transactions recorded during the period: |  |  |  |  |  |
(Losses) gains recognized in earnings (a) |  | (1 | ) |  | 5 |  |  | — |
Net (losses) gains recognized as regulatory assets and liabilities |  | (5 | ) |  | 28 |  |  | 53 |
Balance at Dec. 31 |  | $ | 29 |  |  | $ | 35 |  |  | $ | 17 |
(a) | Amounts relate to commodity derivatives held at the end of the period.
Fair Value, by Balance Sheet Grouping [Table Text Block] | As of Dec. 31, other financial instruments for which the carrying amount did not equal fair value:
|  | 2018 |  | 2017
(Millions of Dollars) |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Long-term debt, including current portion |  | $ | 16,209 |  |  | $ | 16,755 |  |  | $ | 14,977 |  |  | $ | 16,531 |

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- Definition Tabular disclosure of the amortized cost of assets held in rabbi trust. Also includes the fair value of these assets measured on a recurring basis in their entirety and the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets or liabilities (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References No definition available. + Details
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