Fair Value of Financial Assets and Liabilities - Consideration of Credit Risk and Concentrations (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($) Counterparty	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) Counterparty	Jun. 30, 2022 USD ($)
Consideration of Credit Risk and Concentrations [Abstract]
Derivative instruments designated as fair value hedges	$ 0	$ 0	$ 0	$ 0
Other Derivative Instruments
Consideration of Credit Risk and Concentrations [Abstract]
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0	0	(10)	2
Pre-tax gains (losses) recognized during the period in income	(5)	3	(17)	(8)
Natural Gas Commodity | Other Derivative Instruments
Consideration of Credit Risk and Concentrations [Abstract]
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)			(10)	2
Pre-tax gains (losses) recognized during the period in income			(12)	(11)
Commodity Trading | Other Derivative Instruments
Consideration of Credit Risk and Concentrations [Abstract]
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	0	0	0	0
Pre-tax gains (losses) recognized during the period in income	$ (5)	$ 3	$ (5)	$ 3
Credit Concentration Risk
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty	10		10
Credit Concentration Risk | Municipal or Cooperative Entities or Other Utilities [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty	6		6
Credit Concentration Risk | External Credit Rating, Investment Grade [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty	2		2
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties	$ 32		$ 32
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)	38.00%		38.00%
Credit Concentration Risk | External Credit Rating, Non Investment Grade [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty	3		3
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties	$ 14		$ 14
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)	17.00%		17.00%
Credit Concentration Risk | Internal Investment Grade
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty	5		5
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties	$ 20		$ 20
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)	24.00%		24.00%