v3.19.1

Assets and Liabilities with Recurring Fair Value Measurements Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Derivative, Fair Value, Net | [1] | $ (141,000,000) | $ 76,000,000
Physical Power [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Derivative, Fair Value, Net |  | 36,000,000 | 149,000,000
Physical Power [Member] | Minimum [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Fair Value Inputs Quantitative Information |  | 2.12 | 4.13
Physical Power [Member] | Maximum [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Fair Value Inputs Quantitative Information |  | 227.98 | 119.20
Natural Gas [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Derivative, Fair Value, Net |  | (73,000,000) | 34,000,000
Natural Gas [Member] | Minimum [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Fair Value Inputs Quantitative Information |  | 0.75 | 1.62
Natural Gas [Member] | Maximum [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Fair Value Inputs Quantitative Information |  | 8.87 | 13.67
Power Congestion Products [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Derivative, Fair Value, Net |  | 26,000,000 | 11,000,000
Power Congestion Products [Member] | Minimum [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Fair Value Inputs Quantitative Information |  | (11.71) | (10.54)
Power Congestion Products [Member] | Maximum [Member] |  |  |
Quantitative Information about Level 3 fair Value Measurements [Line Items] |  |  |
Fair Value Inputs Quantitative Information |  | $ 11.88 | $ 9.13
[1] | At December 31, 2018 and 2017, we had $244 million and $155 million of collateral under master netting arrangements that were not offset against our derivative instruments on the Consolidated Balance Sheets primarily related to initial margin requirements.

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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 + Details
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