Fair Value of Financial Instruments Financial Assets and Liabilities Recognized at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Assets:
Cash equivalents	$ 92	$ 44
Debt securities:
Domestic government	17	19
Corporate credit	13	14
Money market funds measured at NAV (2)	14	14
Non-qualified benefit plan trust: (2)
Money market funds	1	1
Equity securities - domestic	3	4
Debt securities—domestic government	4	4
Assets from price risk management activities: (1) (3)
Electricity	36	17
Natural gas	292	120
Total	14	14
Assets, Fair Value Disclosure	472	237
Liabilities from price risk management activities: (1) (3)
Electricity	122	123
Natural gas	10	14
Total	132	137
Fair Value, Inputs, Level 1 [Member]
Assets:
Cash equivalents	92	44
Debt securities:
Domestic government	9	9
Corporate credit	0	0
Non-qualified benefit plan trust: (2)
Money market funds	1	1
Equity securities - domestic	3	4
Debt securities—domestic government	4	4
Assets from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	109	62
Liabilities from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	0	0
Fair Value, Inputs, Level 2 [Member]
Assets:
Cash equivalents	0	0
Debt securities:
Domestic government	8	10
Corporate credit	13	14
Non-qualified benefit plan trust: (2)
Money market funds	0	0
Equity securities - domestic	0	0
Debt securities—domestic government	0	0
Assets from price risk management activities: (1) (3)
Electricity	35	16
Natural gas	274	115
Total	330	155
Liabilities from price risk management activities: (1) (3)
Electricity	51	33
Natural gas	10	13
Total	61	46
Fair Value, Inputs, Level 3 [Member]
Assets:
Cash equivalents	0	0
Debt securities:
Domestic government	0	0
Corporate credit	0	0
Non-qualified benefit plan trust: (2)
Money market funds	0	0
Equity securities - domestic	0	0
Debt securities—domestic government	0	0
Assets from price risk management activities: (1) (3)
Electricity	1	1
Natural gas	18	5
Total	19	6
Liabilities from price risk management activities: (1) (3)
Electricity	71	90
Natural gas	0	1
Total	$ 71	$ 91