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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Investments in Unconsolidated Affiliates (Gas Utilities and Infrastructure Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,936	$ 1,409	$ 1,175
Return of investment capital	11	137	281
ACP
Investments In Unconsolidated Affiliates [Line Items]
Return of investment capital	265
Gas Utilities and Infrastructure
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,388	1,003	763
Gas Utilities and Infrastructure \| ACP
Investments In Unconsolidated Affiliates [Line Items]
Ownership interest	47.00%
Investments in equity method unconsolidated affiliates	$ 1,179	797
Gas Utilities and Infrastructure \| Sabal Trail
Investments In Unconsolidated Affiliates [Line Items]
Ownership interest	7.50%
Investments in equity method unconsolidated affiliates	$ 121	112
Return of investment capital		112
Gas Utilities and Infrastructure \| Constitution
Investments In Unconsolidated Affiliates [Line Items]
Ownership interest	24.00%
Investments in equity method unconsolidated affiliates		25
Piedmont
Investments In Unconsolidated Affiliates [Line Items]
Investments in equity method unconsolidated affiliates	$ 83	64
Return of investment capital	$ 4	3	$ 2
Piedmont \| Gas Utilities and Infrastructure \| Cardinal
Investments In Unconsolidated Affiliates [Line Items]
Ownership interest	21.49%
Investments in equity method unconsolidated affiliates	$ 9	10
Piedmont \| Gas Utilities and Infrastructure \| Pine Needle
Investments In Unconsolidated Affiliates [Line Items]
Ownership interest	45.00%
Investments in equity method unconsolidated affiliates	$ 28	13
Piedmont \| Gas Utilities and Infrastructure \| Hardy Storage
Investments In Unconsolidated Affiliates [Line Items]
Ownership interest	50.00%
Investments in equity method unconsolidated affiliates	$ 51	$ 46