Revenue from Contracts with Customers - NPC (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
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
NPC
Disaggregation of Revenue [Line Items]
Operating revenue	802	808	1,731	1,706
NPC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	6	7	16	20
NPC | Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	796	801	1,715	1,686
NPC | Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	768	780	1,658	1,638
NPC | Regulated | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	28	21	57	48
NPC | Customer Revenue | Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	762	772	1,641	1,618
NPC | Customer Revenue | Regulated | Retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	477	495	998	993
NPC | Customer Revenue | Regulated | Retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	129	127	323	317
NPC | Customer Revenue | Regulated | Retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	152	147	310	300
NPC | Customer Revenue | Regulated | Retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	4	3	10	8
NPC | Distribution only service | Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 6	$ 8	$ 17	$ 20