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Fair Value of Financial Assets and Liabilities, Cost and Fair Value of Nuclear Decommissioning Fund (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale Securities, Gross Unrealized Gain |  | $ 450 |  | $ 560 |
Available-for-sale Securities, Gross Unrealized Loss |  | 45 |  | 7 |
Decommissioning Fund Investments, Fair Value |  | 2,055 |  |  |
Investments [Abstract] |  |  |  |  |
Investment in subsidiaries |  | 141 |  | 140 |
Miscellaneous investments |  | 121 |  | 114 |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Cash equivalents |  | 24 | [1] | 29 |
Alternative Investment |  | 819 | [1] | 659 |
Available-for-sale Securities |  |  |  | 2,143 |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Cash equivalents |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Alternative Investment |  | 0 | [1] | 0 |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Commingled Funds |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
AvailableForSaleSecuritiesCommingledFunds | [2] |  |  | 882 |
Alternative Investment |  | 819 | [1] | 659 | [2]
Available-for-sale Securities | [1] | 898 |  |  |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Debt Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Alternative Investment |  | 0 | [1] | 0 | [2]
Debt Securities, Available-for-sale |  | 436 | [1] | 441 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Equity Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Alternative Investment |  | 0 | [1] | 0 | [2]
Available-for-sale Securities, Equity Securities |  | 697 | [1] | 791 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Cash equivalents |  | 24 | [1] | 29 |
Available-for-sale Securities |  | 800 | [1] | 1,043 |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Commingled Funds |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
AvailableForSaleSecuritiesCommingledFunds | [2] |  |  | 223 |
Available-for-sale Securities | [1] | 79 |  |  |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Debt Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-sale |  | 0 | [1] | 0 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 1 | Equity Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale Securities, Equity Securities |  | 697 | [1] | 791 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Cash equivalents |  | 0 | [1] | 0 |
Available-for-sale Securities |  | 436 | [1] | 441 |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Commingled Funds |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
AvailableForSaleSecuritiesCommingledFunds | [2] |  |  | 0 |
Available-for-sale Securities | [1] | 0 |  |  |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Debt Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-sale |  | 436 | [1] | 441 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 2 | Equity Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale Securities, Equity Securities |  | 0 | [1] | 0 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Cash equivalents |  | 0 | [1] | 0 |
Available-for-sale Securities |  | 0 | [1] | 0 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Commingled Funds |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
AvailableForSaleSecuritiesCommingledFunds | [2] |  |  | 0 |
Available-for-sale Securities | [1] | 0 |  |  |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Debt Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-sale |  | 0 | [1] | 0 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Fair Value | Level 3 | Equity Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale Securities, Equity Securities |  | 0 | [1] | 0 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Cash equivalents |  | 24 | [1] | 29 | [2]
Available-for-sale Securities |  | 1,649 | [1] | 1,591 |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Commingled Funds |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
AvailableForSaleSecuritiesCommingledFunds | [2] |  |  | 701 |
Available-for-sale Securities | [1] | 758 |  |  |
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Debt Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Debt Securities, Available-for-sale |  | 466 | [1] | 438 | [2]
Nuclear Decommissioning Fund | Fair Value Measured on a Recurring Basis | Cost | Equity Securities |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Available-for-sale Securities, Equity Securities |  | $ 401 | [1] | $ 423 | [2]
[1] | orted 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 TotalNuclear decommissioning fund (a) Cash equivalents $29 $29 $— $— $— $29Commingled funds 701 223 — — 659 882Debt securities 438 — 441 — — 441Equity securities 423 791 — — — 791Total $1,591 $1,043 $441 $— $659 $2,143
[2] | 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.

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- Definition The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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