Segment and Related Information (Financial Data - Operating Revenues including Inter-segment Revenues) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	$ 1,733	$ 1,864
Operating Revenues — Non-utility operations	1,289	1,650
Operating Revenues	3,022	3,514
Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	(124)	(172)
Operating Revenues	(124)	(172)
Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,216	1,235
Electric | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	1,212	1,235
Operating Revenues — Non-utility operations	4	0
Electric | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(15)	(14)
Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	540	645
Gas | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	540	645
Gas | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(4)	(2)
Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	170	116
Gas Storage and Pipelines | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	170	116
Gas Storage and Pipelines | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(4)	(3)
Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	307	388
Power and Industrial Projects | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	307	388
Power and Industrial Projects | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(94)	(145)
Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	913	1,301
Energy Trading | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	913	1,301
Energy Trading | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(6)	(7)
Corporate and Other | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	0	1
Corporate and Other | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ (1)	$ (1)