Supplemental Cash Flow and Noncash Investing Transactions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Car	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Car
Noncash or Part Noncash Divestitures [Line Items]
Noncash or Part Noncash Acquisition, Debt Assumed	$ 11.6
Capital Lease Obligations Incurred	$ 0.0		$ 14.8
Capital Leases, Future Minimum Payments Due, Next Twelve Months		$ 0.0	$ 17.8
Number of railcars received | Car	1,224		157
Supplemental Cash Flow Information
Interest paid	$ 154.6	145.4	$ 144.4
Income taxes paid (refunded), net	21.5	28.6	13.3
Portfolio proceeds	$ 165.6	$ 223.7	$ 482.2