Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current Income Tax Expense [Abstract]
Federal	$ 201	$ 160	$ 80
State	20	22	19
Total current expense	221	182	99
Deferred Income Tax Expense (Benefit) [Abstract]
Federal	(75)	(69)	146
State	0	0	3
Total deferred expense (benefit)	(75)	(69)	149
Total income tax expense	146	113	248
Income Tax Reconciliation [Abstract]
Income before income taxes and extraordinary item	415	392	736
Federal statutory income tax rate	35.00%	35.00%	35.00%
Expected federal income tax expense	145	137	258
Increase (decrease) in tax expense resulting from:
State income tax expense, net of federal income tax	13	14	15
Amortization of investment tax credit	0	(1)	(6)
Decrease in settled and uncertain tax positions	(5)	(26)	(4)
Other, net	(7)	(11)	(15)
Total	1	(24)	(10)
Total income tax expense	146	113	248
Effective tax rate	35.20%	28.80%	33.70%
Reduction In Liability For Uncertain Tax Positions	5	26
Investment Tax Credit		1
Deferred Tax Assets and Liabilities [Abstract]
Allowance for doubtful accounts	1	1
Other	2	0
Total current deferred tax assets	3	1
Employee benefits	80	95
Other	17	9
Total non-current deferred tax assets	97	104
Total deferred tax assets	100	105
Depreciation	1,166	1,103
Regulatory assets, net	966	1,098
Total deferred tax liabilities	2,132	2,201
Accumulated deferred income taxes, net	2,032	2,096
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, beginning of year	0	44	232
Unrecognized tax benefits related to prior years [Abstract]
Additions	0	0	0
Reductions	0	(46)	(192)
Unrecognized tax positions related to current year [Abstract]
Additions	0	0	4
Settlements	0	2	0
Unrecognized Tax Benefits, end of year	0	0	44
Unrecognized tax benefits that would reduce effective tax rate			18
Unrecognized tax benefits interest on income tax expense	0	(5)	(12)
Unrecognized tax benefits interest on income taxes accrued	$ 6