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