Fair Value of Financial Assets and Liabilities - Consideration of Credit Risk and Concentrations (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2022 USD ($) Counterparty	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) Counterparty	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)
Consideration of Credit Risk and Concentrations [Abstract]
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities					$ 0	$ 0
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	(2)	6
Pre-tax gains (losses) recognized during the period in income		3	10	(8)	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
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)					0
Pre-tax gains (losses) recognized during the period in income					0
Natural Gas Commodity
Consideration of Credit Risk and Concentrations [Abstract]
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities				1
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]			(2)	6
Pre-tax gains (losses) recognized during the period in income	[1],[2]			(11)	(6)
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]	$ 3	$ 10	$ 3	14
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
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)					0
Pre-tax gains (losses) recognized during the period in income					$ 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		5		5
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties		$ 51		$ 51
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		43.00%		43.00%
Credit Concentration Risk | No Investment Grade Ratings from External Credit Rating Agencies [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		$ 19		$ 19
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		16.00%		16.00%
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		2		2
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties		$ 28		$ 28
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		24.00%		24.00%

[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 operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue as appropriate.

[4] Recorded to interest charges.