Revenue from Contracts with Customers - MEC (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 4,199	$ 3,317	$ 8,911	$ 6,833
Operating revenue	6,064	4,612	12,145	9,139
Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	102	102	239	220
MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	690	607	1,752	1,284
Operating revenue	693	613	1,760	1,294
MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1		11
MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	3	6	8	10
Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	3,587	2,969	7,681	6,182
Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2,411	2,172	4,519	4,233
Regulated | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	109	104	607	338
Regulated | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	108	59	301	136
Regulated | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	31	20	56	47
Regulated | MEC | Retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	605	553	1,517	1,149
Regulated | MEC | Retail | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	229	225	698	501
Regulated | MEC | Retail | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	98	88	298	201
Regulated | MEC | Retail | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	233	200	435	367
Regulated | MEC | Retail | Natural gas transportation services
Disaggregation of Revenue [Line Items]
Total Customer Revenue	9	7	19	18
Regulated | MEC | Retail | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	36	33	67	62
Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	69	37	194	101
Regulated | MEC | Multi-value transmission projects | Multi-value transmission projects
Disaggregation of Revenue [Line Items]
Total Customer Revenue	15	17	30	33
Nonregulated | MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue		0		1
Electric | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	586	518	1,131	989
Electric | Regulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	583	513	1,124	981
Operating revenue	586	518	1,131	989
Electric | Regulated | MEC | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	516	468	968	878
Electric | Regulated | MEC | Retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	170	166	331	314
Electric | Regulated | MEC | Retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	80	73	151	143
Electric | Regulated | MEC | Retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	230	197	420	360
Electric | Regulated | MEC | Retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	36	32	66	61
Electric | Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	52	28	126	70
Electric | Regulated | MEC | Multi-value transmission projects | Multi-value transmission projects
Disaggregation of Revenue [Line Items]
Total Customer Revenue	15	17	30	33
Electric | Regulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	3	5	7	8
Natural Gas | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	106	95	618	304
Natural Gas | Regulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	106	94	617	302
Operating revenue	106	95	618	304
Natural Gas | Regulated | MEC | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	89	85	549	271
Natural Gas | Regulated | MEC | Retail gas | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	59	59	367	187
Natural Gas | Regulated | MEC | Retail gas | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	18	15	147	58
Natural Gas | Regulated | MEC | Retail gas | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	3	3	15	7
Natural Gas | Regulated | MEC | Retail gas | Natural gas transportation services
Disaggregation of Revenue [Line Items]
Total Customer Revenue	9	7	19	18
Natural Gas | Regulated | MEC | Retail gas | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	0	1	1	1
Natural Gas | Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	17	9	68	31
Natural Gas | Regulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	0	1	1	2
Other | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	1	0	11	1
Other | Nonregulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	0	11	1
Operating revenue	1	0	11	1
Other | Nonregulated | MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	0	11	1
Other | Nonregulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	$ 0	$ 0	$ 0	$ 0