Railcar Leasing and Management Services Group - Selected consolidating income statement information for the Leasing Group (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Total revenues	$ 973.6	$ 1,111.7	$ 2,756.4	$ 3,484.5
Operating profit:
Total operating profit	153.0	183.6	404.8	578.6
Select expense information:
Depreciation			220.7	210.6
Interest	46.8	45.3	137.5	136.7
Operating Segments
Revenues:
Total revenues	1,199.4	1,401.6	3,404.6	4,472.2
Operating profit:
Total operating profit	209.0	247.3	581.1	811.5
Railcar Leasing and Management Services Group
Revenues:
Total revenues	274.9	173.2	645.4	647.1
Railcar Leasing and Management Services Group | Operating Segments
Revenues:
Total revenues	$ 275.1	173.7	$ 646.1	648.8
Percent Change, Revenues	58.40%		(0.40%)
Operating profit:
Total operating profit	$ 120.6	$ 80.5	$ 316.4	$ 272.4
Percent Change, Operating Profit	49.80%		16.20%
Operating profit margin:
Total operating profit margin	43.80%	46.30%	49.00%	42.00%
Select expense information:
Depreciation	$ 43.3	$ 39.4	$ 128.5	$ 115.5
Percent Change, Depreciation	9.90%		11.30%
Maintenance Costs	$ 25.0	21.3	$ 69.4	84.7
Percent Change, Maintenance	17.40%		(18.10%)
Rent	$ 10.0	9.9	$ 30.0	29.3
Percent Change, Rent	1.00%		2.40%
Interest	$ 32.1	31.2	$ 94.0	94.4
Percent Change, Interest	2.90%		(0.40%)
Railcar Leasing and Management Services Group | Operating Segments | Leasing and management
Revenues:
Total revenues	$ 188.5	173.7	$ 552.4	522.7
Percent Change, Revenues	8.50%		5.70%
Operating profit:
Total operating profit	$ 86.2	$ 80.5	$ 256.8	$ 224.8
Percent Change, Operating Profit	7.10%		14.20%
Operating profit margin:
Total operating profit margin	45.70%	46.30%	46.50%	43.00%
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned one year or less at the time of sale
Revenues:
Total revenues	$ 86.6	$ 0.0	$ 93.7	$ 126.1
Operating profit:
Total operating profit	17.9	0.0	19.4	34.1
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned more than one year at the time of sale
Operating profit:
Total operating profit	$ 16.5	$ 0.0	$ 40.2	$ 13.5