Revenue from Contracts with Customers - NPC (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
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
NPC
Disaggregation of Revenue [Line Items]
Operating revenue	415	370
NPC | Other revenue
Disaggregation of Revenue [Line Items]
Operating revenue	5	5
NPC | Regulated
Disaggregation of Revenue [Line Items]
Total Customer Revenue	410	365
NPC | Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	394	351
NPC | Regulated | Wholesale, transmission and other
Disaggregation of Revenue [Line Items]
Total Customer Revenue	16	14
NPC | Customer Revenue | Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	389	346
NPC | Customer Revenue | Regulated | Retail electric | Residential
Disaggregation of Revenue [Line Items]
Total Customer Revenue	214	196
NPC | Customer Revenue | Regulated | Retail electric | Commercial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	96	84
NPC | Customer Revenue | Regulated | Retail electric | Industrial
Disaggregation of Revenue [Line Items]
Total Customer Revenue	78	63
NPC | Customer Revenue | Regulated | Retail electric | Other retail
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1	3
NPC | Distribution only service | Regulated | Retail electric
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 5	$ 5