Segment and Related Information (Financial Data - Inter-segment Billing) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ (3,284)	$ (3,119)	$ (8,889)	$ (9,521)
Electric
Segment Reporting Information [Line Items]
Revenues	(1,693)	(1,520)	(4,221)	(3,945)
Gas
Segment Reporting Information [Line Items]
Revenues	(173)	(155)	(964)	(1,043)
Gas Storage and Pipelines
Segment Reporting Information [Line Items]
Revenues	(204)	(126)	(546)	(363)
Power and Industrial Projects
Segment Reporting Information [Line Items]
Revenues	(324)	(406)	(850)	(1,196)
Energy Trading
Segment Reporting Information [Line Items]
Revenues	(1,061)	(1,105)	(2,714)	(3,519)
Reconciliation and Eliminations
Segment Reporting Information [Line Items]
Revenues	172	195	408	548
Reconciliation and Eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	16	16	46	43
Reconciliation and Eliminations | Gas
Segment Reporting Information [Line Items]
Revenues	4	3	12	8
Reconciliation and Eliminations | Gas Storage and Pipelines
Segment Reporting Information [Line Items]
Revenues	8	11	17	17
Reconciliation and Eliminations | Power and Industrial Projects
Segment Reporting Information [Line Items]
Revenues	134	160	308	462
Reconciliation and Eliminations | Energy Trading
Segment Reporting Information [Line Items]
Revenues	9	4	23	16
Reconciliation and Eliminations | Corporate and Other
Segment Reporting Information [Line Items]
Revenues	$ 1	$ 1	$ 2	$ 2