The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Investments in Unconsolidated Affiliates (Gas Utilities and Infrastructure Investments) (Details) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	$ 925	$ 1,409	$ 1,175	$ 925
Return of investment capital		137	281	1
Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	566	1,003	763	$ 566
Atlantic Coast Pipeline [Member]
Investments In Unconsolidated Affiliates [Line Items]
Return of investment capital		$ 265
Atlantic Coast Pipeline [Member] \| Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Equity Method Investment, Ownership Percentage		47.00%
Investments in equity method unconsolidated affiliates		$ 797	397
Sabal Trail Transmission Pipeline [Member] \| Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Equity Method Investment, Ownership Percentage		7.50%
Investments in equity method unconsolidated affiliates		$ 112	219
Return of investment capital		$ 112
Constitution Pipeline [Member] \| Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Equity Method Investment, Ownership Percentage		24.00%
Investments in equity method unconsolidated affiliates		$ 25	81
Piedmont Natural Gas [Member]
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates		64	61
Return of investment capital	$ 1	$ 3	2		$ 18
Piedmont Natural Gas [Member] \| Cardinal Pipeline Company, LLC [Member] \| Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Equity Method Investment, Ownership Percentage		21.49%
Investments in equity method unconsolidated affiliates		$ 10	11
Piedmont Natural Gas [Member] \| Pine Needle LNG Company, LLC [Member] \| Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Equity Method Investment, Ownership Percentage		45.00%
Investments in equity method unconsolidated affiliates		$ 13	13
Piedmont Natural Gas [Member] \| Hardy Storage Company, LLC [Member] \| Gas Utilities and Infrastructure [Member]
Investments In Unconsolidated Affiliates [Line Items]
Equity Method Investment, Ownership Percentage		50.00%
Investments in equity method unconsolidated affiliates		$ 46	$ 42