Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								9 Months Ended	12 Months Ended		3 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2011 Predecessor
Income Tax Contingency [Line Items]
Liabilities recorded for interest related to uncertain tax positions					$ 5						$ 5
Current tax provision:
Federal and foreign									173	653	638	104
State and local									26	101	105	11
Total current tax provision									199	754	743	115
Deferred tax expense (benefit):
Federal and foreign									128	(125)	(175)	61
State and local									22	(27)	(26)	15
Total deferred tax expense (benefit)									150	(152)	(201)	76
Income tax expense	142	139	155	166	160	133	113	136	349	602	542	191
Effective income tax rate:
Federal statutory income tax rate (as a percent)									35.00%	35.00%	35.00%	35.00%
State income taxes-net of federal effect (as a percent)									3.50%	3.10%	3.70%	3.40%
Other (as a percent)									0.60%	0.30%	0.30%	0.60%
Effective income tax rate (as a percent)									39.10%	38.40%	39.00%	39.00%
Deferred tax liabilities:
Property, plant and equipment	(1,281)				(1,179)					(1,281)	(1,179)
Intangibles assets	(1,772)				(2,118)					(1,772)	(2,118)
Receivable from an affiliate due to pension plan participation	(462)				(397)					(462)	(397)
Other	(52)				(61)					(52)	(61)
Total deferred tax liabilities	(3,567)				(3,755)					(3,567)	(3,755)
Deferred tax assets:
Payable to affiliate due to post-retirement benefit plan participation	983				982					983	982
Debt premiums	55				67					55	67
Other	229				253					229	253
Total deferred tax assets	1,267				1,302					1,267	1,302
Valuation allowance on deferred tax assets	(12)				(12)					(12)	(12)
Net deferred tax assets	1,255				1,290					1,255	1,290
Net deferred tax liabilities	$ (2,312)				$ (2,465)					$ (2,312)	$ (2,465)