Revenue from Contracts with Customers - MEC (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 4,719	$ 4,712
Operating revenue	6,030	6,081
Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	104	137
MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	987	1,062
Operating revenue	1,005	1,067
MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	10
MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	18	5
Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	4,115	4,094
Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2,256	2,108
Regulated | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	388	498
Regulated | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	236	193
Regulated | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	22	25
Regulated | MEC | Retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	809	912
Regulated | MEC | Retail | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	393	469
Regulated | MEC | Retail | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	162	200
Regulated | MEC | Retail | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	207	202
Regulated | MEC | Retail | Natural gas transportation services
Disaggregation of Revenue [Line Items]
Total Customer Revenue	14	10
Regulated | MEC | Retail | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	33	31
Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	162	125
Regulated | MEC | Multi-value transmission projects | Multi-value transmission projects
Disaggregation of Revenue [Line Items]
Total Customer Revenue	15	15
Regulated electric | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	608	545
Regulated electric | Regulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	591	541
Operating revenue	608	545
Regulated electric | Regulated | MEC | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	472	452
Regulated electric | Regulated | MEC | Retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	168	161
Regulated electric | Regulated | MEC | Retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	74	71
Regulated electric | Regulated | MEC | Retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	198	190
Regulated electric | Regulated | MEC | Retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	32	30
Regulated electric | Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	104	74
Regulated electric | Regulated | MEC | Multi-value transmission projects | Multi-value transmission projects
Disaggregation of Revenue [Line Items]
Total Customer Revenue	15	15
Regulated electric | Regulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	17	4
Regulated natural gas | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	396	512
Regulated natural gas | Regulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	395	511
Operating revenue	396	512
Regulated natural gas | Regulated | MEC | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	337	460
Regulated natural gas | Regulated | MEC | Retail gas | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	225	308
Regulated natural gas | Regulated | MEC | Retail gas | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	88	129
Regulated natural gas | Regulated | MEC | Retail gas | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	9	12
Regulated natural gas | Regulated | MEC | Retail gas | Natural gas transportation services
Disaggregation of Revenue [Line Items]
Total Customer Revenue	14	10
Regulated natural gas | Regulated | MEC | Retail gas | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1
Regulated natural gas | Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	58	51
Regulated natural gas | Regulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	1	1
Other | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	1	10
Other | Nonregulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	10
Operating revenue	1	10
Other | Nonregulated | MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	10
Other | Nonregulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	$ 0	$ 0