Railcar Leasing and Management Services Group - Selected consolidating income statement information for the Leasing Group (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Total revenues	$ 831.3	$ 877.3
Operating profit:
Total operating profit	98.6	115.9
Select expense information:
Depreciation	75.3	72.8
Interest	46.3	45.0
Operating Segments
Revenues:
Total revenues	1,180.4	1,121.2
Operating profit:
Total operating profit	166.7	182.3
Railcar Leasing and Management Services Group
Revenues:
Total revenues	174.3	178.6
Railcar Leasing and Management Services Group | Leasing and management
Revenues:
Total revenues	174.6	178.9
Railcar Leasing and Management Services Group | Railcars owned one year or less at the time of sale
Revenues:
Total revenues	0.0	0.0
Railcar Leasing and Management Services Group | Operating Segments
Revenues:
Total revenues	$ 174.6	178.9
Percent Change, Revenues	(2.40%)
Operating profit:
Total operating profit	$ 71.1	$ 85.0
Percent Change, Operating Profit	(16.40%)
Operating profit margin:
Total operating profit margin	40.70%	47.50%
Select expense information:
Depreciation	$ 45.1	$ 42.1
Percent Change, Depreciation	7.10%
Maintenance Costs	$ 26.4	20.5
Percent Change, Maintenance	28.80%
Rent	$ 10.1	10.1
Percent Change, Rent	0.00%
Interest	$ 31.5	30.6
Percent Change, Interest	2.90%
Railcar Leasing and Management Services Group | Operating Segments | Leasing and management
Revenues:
Total revenues	$ 174.6	178.9
Percent Change, Revenues	(2.40%)
Operating profit:
Total operating profit	$ 69.0	$ 85.0
Percent Change, Operating Profit	(18.80%)
Operating profit margin:
Total operating profit margin	39.50%	47.50%
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned one year or less at the time of sale
Revenues:
Total revenues	$ 0.0	$ 0.0
Operating profit:
Total operating profit	0.0	0.0
Railcar Leasing and Management Services Group | Operating Segments | Railcars owned more than one year at the time of sale
Operating profit:
Total operating profit	$ 2.1	$ 0.0