Risk Management and Hedging Activities - PAC - Balance Sheet Location (Details) - PAC - Commodity derivatives - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Total	$ 149		$ (17)
Cash collateral (payable) receivable	5		24
Total derivatives - net basis	154		7
Other Current Assets
Derivatives, Fair Value [Line Items]
Total	159		27
Cash collateral (payable) receivable	(6)		0
Total derivatives - net basis	153		27
Other Assets
Derivatives, Fair Value [Line Items]
Total	40		6
Cash collateral (payable) receivable	0		0
Total derivatives - net basis	40		6
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Total	(42)		(22)
Cash collateral (payable) receivable	11		15
Total derivatives - net basis	(31)		(7)
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total	(8)		(28)
Cash collateral (payable) receivable	0		9
Total derivatives - net basis	(8)		(19)
Not Designated as Hedging
Derivatives, Fair Value [Line Items]
Derivative asset, gross	204		36
Derivative liability	(55)		(53)
Total	149		(17)
Net regulatory asset (liability) on derivative contracts	(149)	$ (102)	17	$ 9	$ 68	$ 62
Not Designated as Hedging | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross	159		29
Derivative liability	0		(2)
Total	159		27
Not Designated as Hedging | Other Assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross	40		6
Derivative liability	0		0
Total	40		6
Not Designated as Hedging | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative asset, gross	4		1
Derivative liability	(46)		(23)
Total	(42)		(22)
Not Designated as Hedging | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative asset, gross	1		0
Derivative liability	(9)		(28)
Total	$ (8)		$ (28)