Segment and Related Information (Financial Data - Inter-segment Billing) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ (3,022)	$ (3,514)
Electric
Segment Reporting Information [Line Items]
Revenues	(1,216)	(1,235)
Gas
Segment Reporting Information [Line Items]
Revenues	(540)	(645)
Gas Storage and Pipelines
Segment Reporting Information [Line Items]
Revenues	(170)	(116)
Power and Industrial Projects
Segment Reporting Information [Line Items]
Revenues	(307)	(388)
Energy Trading
Segment Reporting Information [Line Items]
Revenues	(913)	(1,301)
Reconciliation and Eliminations
Segment Reporting Information [Line Items]
Revenues	124	172
Reconciliation and Eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	15	14
Reconciliation and Eliminations | Gas
Segment Reporting Information [Line Items]
Revenues	4	2
Reconciliation and Eliminations | Gas Storage and Pipelines
Segment Reporting Information [Line Items]
Revenues	4	3
Reconciliation and Eliminations | Power and Industrial Projects
Segment Reporting Information [Line Items]
Revenues	94	145
Reconciliation and Eliminations | Energy Trading
Segment Reporting Information [Line Items]
Revenues	6	7
Reconciliation and Eliminations | Corporate and Other
Segment Reporting Information [Line Items]
Revenues	$ 1	$ 1