Income Taxes Other Income Tax Matters (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Current Federal Tax Expense (Benefit)		$ (16)	$ (34)	$ 1
Deferred tax expense (benefit) excluding selected items		344	320	(2,939)
Amortization and adjustments to deferred income taxes on income tax regulatory assets and liabilities		(206)	(102)	3,583
Other Comprehensive Income (Loss), Tax		5	0	(4)
Deferred Income Tax Expense (Benefit)		143	218	640
Current State and Local Tax Expense (Benefit)		4	8	(11)
Current Change In Unrecognized Tax Expense (Benefit)		2	(6)	(83)
Deferred Federal Income Tax Expense (Benefit)		55	122	460
Deferred State and Local Income Tax Expense (Benefit)		83	85	107
Deferred Change In Unrecognized Tax Expense (Benefit)		5	11	73
Deferred investment tax credits		5	5	5
Income Tax Expense (Benefit)		128	181	$ 542
Internal Revenue Service (IRS) [Member]
Income Tax Examination [Line Items]
Tax Credit Carryforward, Amount		639	553
Tax Credit Carryforward, Valuation Allowance		0	5
State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Federal detriment		24	24
Operating Loss Carryforwards		937	1,104
Operating Loss Carryforwards, Valuation Allowance		19	50
Tax Credit Carryforward Net Of Federal Detriment	[1]	89	89
Valuation Allowance for Tax Credit Carryforward Net of Federal Benefit	[2]	66	69
Federal Benefit		$ 17	$ 18

[1] State tax credit carryforwards are net of federal detriment of $24 million as of Dec. 31, 2019 and 2018.

[2] Valuation allowances for state tax credit carryforwards were net of federal benefit of $17 million and $18 million as of Dec. 31, 2019 and 2018, respectively.