Income Taxes (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Tax credits percentage of qualified maintenance expenditures to reduce federal income tax	50.00%
Tax credits limitation per mile on maintenance expenditures to reduce federal income tax	$ 3,500
Tax benefit from short line tax credit		45,000,000
Provision for income taxes	22,900,000	(24,932,000)
Effective income tax rate	36.60%
Income tax expense, other than the short line tax credits		20,000,000
Provision for income tax as a percentage of income before income taxes other than the short line tax credits		34.70%
Related to full year 2012 [Member]
Tax benefit from extension of the short line tax credit		41,000,000
Related to quarter [Member]
Tax benefit from extension of the short line tax credit		$ 4,000,000