Segment and Related Information (Financial Data - Operating Revenues including Inter-segment Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	$ 1,656	$ 1,669	$ 4,937	$ 4,923
Operating Revenues — Non-utility operations	1,463	1,881	4,584	5,539
Operating Revenues	3,119	3,550	9,521	10,462
Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	(195)	(201)	(548)	(585)
Operating Revenues	(195)	(201)	(548)	(585)
Electric
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,520	1,521	3,945	4,002
Electric | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	1,520	1,521	3,945	4,002
Electric | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(16)	(13)	(43)	(39)
Gas
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	155	164	1,043	969
Gas | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Utility operations	155	164	1,043	969
Gas | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(3)	(3)	(8)	(9)
Gas Storage and Pipelines
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	126	122	363	363
Gas Storage and Pipelines | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	126	122	363	363
Gas Storage and Pipelines | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(11)	(7)	(17)	(29)
Power and Industrial Projects
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	406	612	1,196	1,717
Power and Industrial Projects | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	406	612	1,196	1,717
Power and Industrial Projects | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(160)	(171)	(462)	(488)
Energy Trading
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	1,105	1,332	3,519	3,994
Energy Trading | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	1,105	1,332	3,519	3,994
Energy Trading | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	(4)	(6)	(16)	(18)
Corporate and Other | Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues — Non-utility operations	2	0	3	2
Corporate and Other | Reconciliation and Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating Revenues	$ (1)	$ (1)	$ (2)	$ (2)