Revenues (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 2,880	$ 3,048	$ 2,658	$ 2,951	$ 2,796	$ 3,017	$ 2,645	$ 2,946	$ 11,537	$ 11,404	$ 11,107
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									11,020
Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									9,508
Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									3,945
Retail | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									5,423
Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									140
Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									791
Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									523
Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									198
Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues									517
Regulated Electric | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									9,339
Regulated Electric | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									7,927
Regulated Electric | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									2,919
Regulated Electric | Retail | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									4,874
Regulated Electric | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									134
Regulated Electric | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									791
Regulated Electric | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									523
Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									98
Regulated Electric | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues									380
Regulated Natural Gas | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									1,612
Regulated Natural Gas | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									1,512
Regulated Natural Gas | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									988
Regulated Natural Gas | Retail | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									524
Regulated Natural Gas | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									0
Regulated Natural Gas | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									0
Regulated Natural Gas | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									0
Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									100
Regulated Natural Gas | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues									127
All Other | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									69
All Other | Retail
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									69
All Other | Retail | Residential
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									38
All Other | Retail | Commercial and industrial (C&I)
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									25
All Other | Retail | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									6
All Other | Wholesale
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									0
All Other | Transmission
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									0
All Other | Other
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers									0
All Other | Alternative revenue and other
Disaggregation of Revenue [Line Items]
Total operating revenues									10
Operating Segments
Disaggregation of Revenue [Line Items]
Total operating revenues									11,537
Operating Segments | Regulated Electric
Disaggregation of Revenue [Line Items]
Total operating revenues									9,719
Operating Segments | Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total operating revenues									1,739
Operating Segments | All Other
Disaggregation of Revenue [Line Items]
Total operating revenues									$ 79