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Fair Value of FInancial Instruments Fair Value Unobservable Input Reconciliation (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |
Net realized and unrealized losses | $ 35,000,000 | $ 11,000,000 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 | (1,000,000) |
Net transfers out of Level 3 to Level 2 | (15,000,000) | (10,000,000) |
Net liabilities from price risk management activities as of end of year | 139,000,000 | 119,000,000 | $ 119,000,000
Level 3 net unrealized losses that have been fully offset by the effect of regulatory accounting | 41,000,000 | 11,000,000 |
Net realized losses | $ 6,000,000 | $ 0 |

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- Definition Level 3 net realized and unrealized losses that have been offset by the effect of regulatory accounting. + References No definition available. + Details
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- Definition Net Liabilities From Price Risk Management Activities Classified as Level 3 + References No definition available. + Details
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- Definition Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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