Railcar Leasing and Management Services Group - Selected consolidating income statement information for the Leasing Group (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 942.3	$ 905.5	$ 1,773.6	$ 1,782.8
Operating profit:
Total operating profit	125.5	134.6	224.1	250.5
Select expense information:
Depreciation			152.6	146.5
Interest	43.8	45.7	90.1	90.7
Operating Segments
Revenues:
Total revenues	1,209.7	1,084.0	2,390.1	2,205.2
Operating profit:
Total operating profit	193.9	188.6	360.6	370.9
Railcar Leasing and Management Services Group
Revenues:
Total revenues	213.2	191.9	387.5	370.5
Railcar Leasing and Management Services Group | Leasing and management
Revenues:
Total revenues	184.2	185.0	358.8	363.9
Railcar Leasing and Management Services Group | Railcars owned one year or less at the time of sale
Revenues:
Total revenues	29.2	7.1	29.2	7.1
Railcar Leasing and Management Services Group | Operating Segments
Revenues:
Total revenues	$ 213.4	192.1	$ 388.0	371.0
Percent Change, Revenues	11.10%		4.60%
Operating profit:
Total operating profit	$ 91.8	$ 110.8	$ 162.9	$ 195.8
Percent Change, Operating Profit	(17.10%)		(16.80%)
Operating profit margin:
Total operating profit margin	43.00%	57.70%	42.00%	52.80%
Select expense information:
Depreciation	$ 47.0	$ 43.1	$ 92.1	$ 85.2
Percent Change, Depreciation	9.00%		8.10%
Maintenance Costs	$ 25.0	23.9	$ 51.4	44.4
Percent Change, Maintenance	4.60%		15.80%
Rent	$ 9.9	9.9	$ 20.0	20.0
Percent Change, Rent	0.00%		0.00%
Interest	$ 32.3	31.3	$ 63.8	61.9
Percent Change, Interest	3.20%		3.10%
Railcar Leasing and Management Services Group | Operating Segments | Leasing and management
Revenues:
Total revenues	$ 184.2	185.0	$ 358.8	363.9
Percent Change, Revenues	(0.40%)		(1.40%)
Operating profit:
Total operating profit	$ 77.9	$ 85.6	$ 146.9	$ 170.6
Percent Change, Operating Profit	(9.00%)		(13.90%)
Operating profit margin:
Total operating profit margin	42.30%	46.30%	40.90%	46.90%
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned one year or less at the time of sale
Revenues:
Total revenues	$ 29.2	$ 7.1	$ 29.2	$ 7.1
Operating profit:
Total operating profit	4.4	1.5	4.4	1.5
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned more than one year at the time of sale
Operating profit:
Total operating profit	$ 9.5	$ 23.7	$ 11.6	$ 23.7