Quarterly Financial Data Items affecting quarter results (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
After-tax gain on sale of assets	$ 1.0	$ 0.9	$ 1.0	$ 0.5	$ 0.8	$ 0.5	$ 0.7	$ 1.3
After-tax business development and related costs	1.0	0.5	1.0	0.7	0.7		0.7	0.4
After-tax credit facility refinancing-related costs			2.9
Tax benefit from retroactive change in tax accounting method related to acquired companies		3.9							3.9
Tax benefit related to final tax returns filed	3.5	0.7				1.7
Tax benefit associated with the United States Short Line Tax Credit	7.4				7.6	6.8	7.5	4.0
After-tax impact of RailAmerica integration and acquisition-related costs					0.6	1.3		8.0
After tax impact of depreciation and amortization expense as a result of the finalization of the allocation of fair values to RailAmerica's assets and liabilities						1.3
Tax valuation allowance on foreign tax credits generated in prior years					2.0
Q1-Q3 2014 [Member]
Tax benefit associated with the United States Short Line Tax Credit	19.6
Related to prior fiscal year reported in current fiscal year [Member]
Tax benefit related to the retroactive extension of the United States Short Line Tax Credit								$ 41.0