Segment and Related Information (Financial Data - Operating Revenues including Inter-segment Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	$ 1,542	$ 1,417	$ 3,275	$ 3,281
Operating Revenues — Non-utility operations	1,041	1,471	2,330	3,121
Operating Revenues	2,583	2,888	5,605	6,402
Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	(112)	(181)	(236)	(353)
Operating Revenues	(112)	(181)	(236)	(353)
Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,312	1,190	2,528	2,425
Electric | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	1,309	1,190	2,521	2,425
Operating Revenues — Non-utility operations	3	0	7	0
Electric | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(15)	(13)	(30)	(27)
Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	251	243	791	888
Gas | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	251	243	791	888
Gas | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(4)	(3)	(8)	(5)
Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	172	121	342	237
Gas Storage and Pipelines | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	172	121	342	237
Gas Storage and Pipelines | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(5)	(3)	(9)	(6)
Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	219	402	526	790
Power and Industrial Projects | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	219	402	526	790
Power and Industrial Projects | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(80)	(157)	(174)	(302)
Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	740	1,113	1,653	2,414
Energy Trading | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	740	1,113	1,653	2,414
Energy Trading | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(8)	(5)	(14)	(12)
Corporate and Other | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	1	0	1	1
Corporate and Other | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ 0	$ 0	$ (1)	$ (1)