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Related Party Transactions (Equity Method Investments) (Details) - Piedmont Natural Gas [Member] - Equity Method Investee [Member] - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Related Party Transaction [Line Items] |  |  |  |
Related party transaction, expenses from transactions with related party | $ 6 | $ 6 | $ 18 | $ 19
Cardinal Pipeline Company, LLC [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Related party transaction, expenses from transactions with related party | 2 | 2 | 5 | 6
Pine Needle LNG Company, LLC [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Related party transaction, expenses from transactions with related party | 2 | 2 | 6 | 6
Hardy Storage Company, LLC [Member] |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Related party transaction, expenses from transactions with related party | $ 2 | $ 2 | $ 7 | $ 7

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- Definition Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 + Details
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- Details
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- Details
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