Segment and Related Information (Financial Data - Inter-segment Billing) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Operating Revenues	$ (3,778)	$ (3,022)
Electric
Segment Reporting Information [Line Items]
Operating Revenues	(1,364)	(1,216)
Gas
Segment Reporting Information [Line Items]
Operating Revenues	(612)	(540)
Gas Storage and Pipelines
Segment Reporting Information [Line Items]
Operating Revenues	(197)	(170)
Power and Industrial Projects
Segment Reporting Information [Line Items]
Operating Revenues	(366)	(407)
Energy Trading
Segment Reporting Information [Line Items]
Operating Revenues	(1,439)	(913)
Reconciliation and Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	201	124
Reconciliation and Eliminations | Electric
Segment Reporting Information [Line Items]
Operating Revenues	16	15
Reconciliation and Eliminations | Gas
Segment Reporting Information [Line Items]
Operating Revenues	4	4
Reconciliation and Eliminations | Gas Storage and Pipelines
Segment Reporting Information [Line Items]
Operating Revenues	5	4
Reconciliation and Eliminations | Power and Industrial Projects
Segment Reporting Information [Line Items]
Operating Revenues	162	94
Reconciliation and Eliminations | Energy Trading
Segment Reporting Information [Line Items]
Operating Revenues	13	6
Reconciliation and Eliminations | Corporate and Other
Segment Reporting Information [Line Items]
Operating Revenues	$ 1	$ 1