Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2015
Asset Impairment Charges									$ 9.0	$ 8.6	$ 38.5
Nonoperating Income, Residual Sharing Income									2.5	10.2	83.6
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Amount									1.4	0.0	7.8
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property									79.4	52.5	52.9
State deferred tax rate change impact										5.0	0.0
Revaluation of deferred tax liabilities	$ 17.9				$ 315.9				9.4	(371.4)	0.0
Selected Quarterly Financial Data (unaudited)
Revenues	356.4	$ 349.7	$ 349.5	$ 305.3	352.8	$ 359.6	$ 348.4	$ 316.1	1,360.9	1,376.9	1,418.3
Net income	$ 49.2	$ 47.0	$ 38.8	$ 76.3	$ 342.1	$ 49.0	$ 53.4	$ 57.5	$ 211.3	$ 502.0	$ 257.1
Share Data
Basic earnings per share (in dollars per share)	$ 1.32	$ 1.25	$ 1.03	$ 2.02	$ 8.98	$ 1.27	$ 1.37	$ 1.46	$ 5.62	$ 12.95	$ 6.35
Diluted earnings per share (in dollars per share)	$ 1.30	$ 1.22	$ 1.01	$ 1.98	$ 8.83	$ 1.25	$ 1.35	$ 1.44	$ 5.52	$ 12.75	$ 6.29
Rail International [Member]
Asset Impairment Charges									$ 3.9	$ 0.3	$ 0.6
Nonoperating Income, Residual Sharing Income									0.0	0.0	0.0
Selected Quarterly Financial Data (unaudited)
Revenues									217.5	197.1	189.0
Portfolio Management [Member]
Asset Impairment Charges									4.5	3.7	6.7
Nonoperating Income, Residual Sharing Income									1.1	9.6	82.8
Selected Quarterly Financial Data (unaudited)
Revenues									16.1	29.9	56.6
Rail North America [Member]
Asset Impairment Charges									0.6	4.6	31.2
Nonoperating Income, Residual Sharing Income									1.4	0.6	0.8
Selected Quarterly Financial Data (unaudited)
Revenues									$ 941.5	$ 977.4	1,018.5
Foreign Tax Authority [Member]
Equity Method Investment, Summarized Financial Information, Income Tax											$ 3.9
Cardinal Marine [Domain]
Number Of Vessels												50.00%