Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Liabilities recorded for interest related to uncertain tax positions											$ 5
Current tax provision:
Federal and foreign									738	653	638
State and local									129	101	105
Total current tax provision									867	754	743
Deferred tax expense:
Federal and foreign									(209)	(125)	(175)
State and local									(19)	(27)	(26)
Total deferred tax expense									(228)	(152)	(201)
Income tax expense	161	156	162	160	142	139	155	166	639	602	542
Effective income tax rate:
Federal statutory income tax rate (as a percent)									35.00%	35.00%	35.00%
State income taxes-net of federal effect (as a percent)									4.00%	3.10%	3.70%
Other (as a percent)									0.70%	0.30%	0.30%
Effective income tax rate (as a percent)									39.70%	38.40%	39.00%
Deferred tax liabilities:
Property, plant and equipment	(1,380)				(1,281)				(1,380)	(1,281)
Intangibles assets	(1,449)				(1,772)				(1,449)	(1,772)
Receivable from an affiliate due to pension plan participation	(500)				(462)				(500)	(462)
Other	(52)				(52)				(52)	(52)
Total deferred tax liabilities	(3,381)				(3,567)				(3,381)	(3,567)
Deferred tax assets:
Payable to affiliate due to post-retirement benefit plan participation	998				983				998	983
Debt premiums	36				55				36	55
Other	275				229				275	229
Total deferred tax assets	1,309				1,267				1,309	1,267
Valuation allowance on deferred tax assets	(12)				(12)				(12)	(12)
Net deferred tax assets	1,297				1,255				1,297	1,255
Net deferred tax liabilities	$ (2,084)				$ (2,312)				$ (2,084)	$ (2,312)