Variable Interest Entities (Narrative) (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Variable Interest Entities [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,864,000,000	$ 1,409,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Variable interest entity, financial or other support, amount	0	0
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,442,000,000	1,060,000,000
Cinergy Receivables [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Percent of proceeds received as cash	75.00%
Percent of proceeds received as subordinated note	25.00%
Minimum equity balance required by Cinergy Receivables	$ 3,000,000
Pioneer Transmission [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Variable interest entity ownership interest	50.00%
Investments in equity method unconsolidated affiliates	$ 55,000,000
OVEC [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Variable interest entity ownership interest	9.00%
Atlantic Coast Pipeline [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,127,000,000	$ 797,000,000
Atlantic Coast Pipeline [Member] | Financial Guarantee [Member]
Variable Interest Entities [Line Items]
Maximum potential amount of future payments associated with guarantees	$ 802,000,000
Percentage of potential amount of future payments associated with guarantees as percent of outstanding borrowings	47.00%