Revenue from Contracts with Customers - MEC (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 5,138	$ 4,357	$ 14,049	$ 11,190
Operating revenue	6,968	6,193	19,113	15,332
Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	87	94	326	314
MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	950	806	2,702	2,090
Operating revenue	966	812	2,726	2,106
MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2		13
MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	16	6	24	16
Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	4,430	3,927	12,111	10,109
Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	3,096	2,981	7,615	7,214
Regulated | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	100	84	707	422
Regulated | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	203	130	504	266
Regulated | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	24	42	80	89
Regulated | MEC | Retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	820	732	2,337	1,881
Regulated | MEC | Retail | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	307	287	1,005	788
Regulated | MEC | Retail | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	124	112	422	313
Regulated | MEC | Retail | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	326	282	761	649
Regulated | MEC | Retail | Natural gas transportation services
Disaggregation of Revenue [Line Items]
Total Customer Revenue	9	8	28	26
Regulated | MEC | Retail | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	54	43	121	105
Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	113	56	307	157
Regulated | MEC | Multi-value transmission projects | Multi-value transmission projects
Disaggregation of Revenue [Line Items]
Total Customer Revenue	15	14	45	47
Nonregulated | MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue		4		5
Regulated electric | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	854	728	1,985	1,717
Regulated electric | Regulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	839	722	1,963	1,703
Operating revenue	854	728	1,985	1,717
Regulated electric | Regulated | MEC | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	736	662	1,704	1,540
Regulated electric | Regulated | MEC | Retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	255	241	586	555
Regulated electric | Regulated | MEC | Retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	107	99	258	242
Regulated electric | Regulated | MEC | Retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	321	280	741	640
Regulated electric | Regulated | MEC | Retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	53	42	119	103
Regulated electric | Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	88	46	214	116
Regulated electric | Regulated | MEC | Multi-value transmission projects | Multi-value transmission projects
Disaggregation of Revenue [Line Items]
Total Customer Revenue	15	14	45	47
Regulated electric | Regulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	15	6	22	14
Regulated natural gas | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	110	80	728	384
Regulated natural gas | Regulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	109	80	726	382
Operating revenue	110	80	728	384
Regulated natural gas | Regulated | MEC | Retail gas
Disaggregation of Revenue [Line Items]
Total Customer Revenue	84	70	633	341
Regulated natural gas | Regulated | MEC | Retail gas | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	52	46	419	233
Regulated natural gas | Regulated | MEC | Retail gas | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	17	13	164	71
Regulated natural gas | Regulated | MEC | Retail gas | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	5	2	20	9
Regulated natural gas | Regulated | MEC | Retail gas | Natural gas transportation services
Disaggregation of Revenue [Line Items]
Total Customer Revenue	9	8	28	26
Regulated natural gas | Regulated | MEC | Retail gas | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	1	2	2
Regulated natural gas | Regulated | MEC | Wholesale
Disaggregation of Revenue [Line Items]
Total Customer Revenue	25	10	93	41
Regulated natural gas | Regulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	1	0	2	2
Other | MEC
Disaggregation of Revenue [Line Items]
Operating revenue	2	4	13	5
Other | Nonregulated | MEC
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2	4	13	5
Operating revenue	2	4	13	5
Other | Nonregulated | MEC | Other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	2	4	13	5
Other | Nonregulated | MEC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	$ 0	$ 0	$ 0	$ 0