Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 3,119	$ 3,550	$ 9,521	$ 10,462
Electric
Disaggregation of Revenue [Line Items]
Revenues	1,520	1,521	3,945	4,002
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	5	6	14	15
Electric | Residential
Disaggregation of Revenue [Line Items]
Revenues	791	773	1,839	1,943
Electric | Commercial
Disaggregation of Revenue [Line Items]
Revenues	515	495	1,358	1,370
Electric | Industrial
Disaggregation of Revenue [Line Items]
Revenues	175	173	497	527
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	39	80	251	162
Gas
Disaggregation of Revenue [Line Items]
Revenues	155	164	1,043	969
Gas | Alternative Revenue Programs
Disaggregation of Revenue [Line Items]
Revenues				4
Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	2	2	6	6
Gas | Other
Disaggregation of Revenue [Line Items]
Revenues	18	32	102	37
Gas | Gas sales
Disaggregation of Revenue [Line Items]
Revenues	87	89	727	726
Gas | End User Transportation
Disaggregation of Revenue [Line Items]
Revenues	35	34	157	168
Gas | Intermediate Transportation
Disaggregation of Revenue [Line Items]
Revenues	15	9	57	38
Gas Storage and Pipelines
Disaggregation of Revenue [Line Items]
Revenues	126	122	363	363
Lease revenue outside scope of Topic 606	2		7
Power and Industrial Projects
Disaggregation of Revenue [Line Items]
Revenues	406	612	1,196	1,717
Lease revenue outside scope of Topic 606	33	37	94	93
Energy Trading
Disaggregation of Revenue [Line Items]
Revenues	1,105	1,332	3,519	3,994
Gain (loss) on derivative outside scope of Topic 606	$ 791	$ 1,100	$ 2,600	$ 3,200