Fair Value of Financial Assets and Liabilities - Consideration of Credit Risk and Concentrations (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023 USD ($) Counterparty	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) Counterparty	Sep. 30, 2022 USD ($)
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]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0	0	0	0
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		2	2	(15)	(8)
Designated as Hedging Instrument | Cash Flow Hedges
Consideration of Credit Risk and Concentrations [Abstract]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		1	1	1	1
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		0	0	0	0
Natural Gas Commodity | Other Derivative Instruments
Consideration of Credit Risk and Concentrations [Abstract]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net				0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	[1]			(10)	2
Pre-tax gains (losses) recognized during the period in income	[1],[2]			(12)	(11)
Commodity Trading | Other Derivative Instruments
Consideration of Credit Risk and Concentrations [Abstract]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		0	0	0	0
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	[3]	2	2	(3)	3
Interest Rate | Designated as Hedging Instrument | Cash Flow Hedges
Consideration of Credit Risk and Concentrations [Abstract]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	[4]	1	1	1	1
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		$ 0	$ 0	$ 0	$ 0
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		7		7
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		4		4
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)		45.00%		45.00%
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		0		0
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		6		6
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties		$ 25		$ 25
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		35.00%		35.00%

[1] Recorded to cost of natural gas sold and transported. These losses are subject to cost-recovery mechanisms and reclassified out of income to a regulatory asset, as appropriate.

[2] Relates primarily to option premium amortization

[3] Recorded to electric revenues. Presented amounts do not reflect non-derivative transactions or margin sharing with customers.

[4] Recorded to interest charges.