Risk Management and Hedging Activities - PAC - Balance Sheet Location (Details) - PAC - Commodity derivatives - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Total	$ 102		$ (17)
Cash collateral (payable) receivable	(11)		24
Total derivatives - net basis	91		7
Other Current Assets
Derivatives, Fair Value [Line Items]
Total	115		27
Cash collateral (payable) receivable	(16)		0
Total derivatives - net basis	99		27
Other Assets
Derivatives, Fair Value [Line Items]
Total	22		6
Cash collateral (payable) receivable	0		0
Total derivatives - net basis	22		6
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Total	(19)		(22)
Cash collateral (payable) receivable	5		15
Total derivatives - net basis	(14)		(7)
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Total	(16)		(28)
Cash collateral (payable) receivable	0		9
Total derivatives - net basis	(16)		(19)
Not Designated as Hedging
Derivatives, Fair Value [Line Items]
Derivative asset, gross	148		36
Derivative liability	(46)		(53)
Total	102		(17)
Net regulatory asset (liability) on derivative contracts	(102)	$ 0	17	$ 68	$ 84	$ 62
Not Designated as Hedging | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross	118		29
Derivative liability	(3)		(2)
Total	115		27
Not Designated as Hedging | Other Assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross	23		6
Derivative liability	(1)		0
Total	22		6
Not Designated as Hedging | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative asset, gross	7		1
Derivative liability	(26)		(23)
Total	(19)		(22)
Not Designated as Hedging | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative asset, gross	0		0
Derivative liability	(16)		(28)
Total	$ (16)		$ (28)