Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 3,148	$ 3,119	$ 2,888	$ 3,514	$ 3,750	$ 3,550	$ 3,159	$ 3,753	$ 12,669	$ 14,212	$ 12,607
Lease revenue outside scope of Topic 606									193
Electric
Disaggregation of Revenue [Line Items]
Revenues									5,229	5,298
Electric | Alternative Revenue Programs
Disaggregation of Revenue [Line Items]
Revenues									22	21
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues									19	20
Electric | Residential
Disaggregation of Revenue [Line Items]
Revenues									2,427	2,494
Electric | Commercial
Disaggregation of Revenue [Line Items]
Revenues									1,795	1,794
Electric | Industrial
Disaggregation of Revenue [Line Items]
Revenues									659	690
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues									348	320
Gas
Disaggregation of Revenue [Line Items]
Revenues									1,482	1,436
Gas | Alternative Revenue Programs
Disaggregation of Revenue [Line Items]
Revenues									8	2
Gas | Other
Disaggregation of Revenue [Line Items]
Revenues									7	7
Gas | Other
Disaggregation of Revenue [Line Items]
Revenues									142	91
Gas | Gas sales
Disaggregation of Revenue [Line Items]
Revenues									1,043	1,055
Gas | End User Transportation
Disaggregation of Revenue [Line Items]
Revenues									219	232
Gas | Intermediate Transportation
Disaggregation of Revenue [Line Items]
Revenues									78	58
Gas Storage and Pipelines
Disaggregation of Revenue [Line Items]
Revenues									501	485
Lease revenue outside scope of Topic 606									9
Power and Industrial Projects
Disaggregation of Revenue [Line Items]
Revenues									1,560	2,204
Lease revenue outside scope of Topic 606									121
Lease revenue outside scope of Topic 606										125
Energy Trading
Disaggregation of Revenue [Line Items]
Revenues									4,610	5,557
Gain (loss) on derivative outside scope of Topic 606									$ 3,400	$ 4,500