Segment and Related Information (Financial Data - Operating Revenues including Inter-segment Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	$ 1,844	$ 1,656	$ 5,119	$ 4,937
Operating Revenues — Non-utility operations	1,440	1,463	3,770	4,584
Operating Revenues	3,284	3,119	8,889	9,521
Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	(172)	(195)	(408)	(548)
Operating Revenues	(172)	(195)	(408)	(548)
Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,693	1,520	4,221	3,945
Electric | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	1,690	1,520	4,211	3,945
Operating Revenues — Non-utility operations	3	0	10	0
Electric | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(16)	(16)	(46)	(43)
Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	173	155	964	1,043
Gas | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	173	155	964	1,043
Gas | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(4)	(3)	(12)	(8)
Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	204	126	546	363
Gas Storage and Pipelines | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	204	126	546	363
Gas Storage and Pipelines | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(8)	(11)	(17)	(17)
Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	324	406	850	1,196
Power and Industrial Projects | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	324	406	850	1,196
Power and Industrial Projects | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(134)	(160)	(308)	(462)
Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,061	1,105	2,714	3,519
Energy Trading | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	1,061	1,105	2,714	3,519
Energy Trading | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(9)	(4)	(23)	(16)
Corporate and Other | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	1	2	2	3
Corporate and Other | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ (1)	$ (1)	$ (2)	$ (2)