Financial Statements for Guarantors of the Senior Notes - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net income	$ 65.5	$ 54.0	$ 107.1	$ 105.7
Equity in earnings of subsidiaries, net of taxes	0.0	0.0	0.0	0.0
Other			241.2	230.4
Net cash provided (required) by operating activities			348.3	336.1
Investing activities:
(Increase) decrease in short-term marketable securities			294.5	55.1
Proceeds from dispositions of property and other assets			5.5	6.0
Proceeds from railcar lease fleet sales owned more than one year			56.4	92.4
Capital expenditures – leasing			(503.2)	(271.6)
Capital expenditures – manufacturing and other			(33.9)	(43.4)
Acquisitions, net of cash acquired			(25.0)	(5.3)
(Increase) decrease in investment in partially-owned subsidiaries			0.0	0.0
Other			1.3	(2.1)
Net cash provided (required) by investing activities			(204.4)	(168.9)
Financing activities:
Payments to retire debt			(674.6)	(98.3)
Proceeds from issuance of debt			478.0	299.4
Shares repurchased			(102.2)	(41.9)
Dividends paid to common shareholders			(39.3)	(33.5)
Purchase of shares to satisfy employee tax on vested stock			(11.3)	(14.0)
Distributions to noncontrolling interest			(10.3)	(16.9)
Distributions to controlling interest in partially-owned subsidiaries			0.0	0.0
Change in intercompany financing between entities			0.0	0.0
Other			(3.1)	(0.1)
Net cash provided (required) by financing activities			(362.8)	94.7
Net increase (decrease) in cash, cash equivalents, and restricted cash			(218.9)	261.9
Cash, cash equivalents, and restricted cash at beginning of period			973.8	741.6
Cash, cash equivalents, and restricted cash at end of period	754.9	1,003.5	754.9	1,003.5
Reportable legal entities | Parent
Operating activities:
Net income	64.1	51.1	104.3	97.1
Equity in earnings of subsidiaries, net of taxes	(97.4)	(103.1)	(181.6)	(162.3)
Other			(12.1)	(11.4)
Net cash provided (required) by operating activities			(89.4)	(76.6)
Investing activities:
(Increase) decrease in short-term marketable securities			294.5	55.1
Proceeds from dispositions of property and other assets			0.1	0.0
Proceeds from railcar lease fleet sales owned more than one year			0.0	0.0
Capital expenditures – leasing			0.0	0.0
Capital expenditures – manufacturing and other			(2.6)	(5.0)
Acquisitions, net of cash acquired			0.0	0.0
(Increase) decrease in investment in partially-owned subsidiaries			0.0	0.0
Other			0.0	0.0
Net cash provided (required) by investing activities			292.0	50.1
Financing activities:
Payments to retire debt			(619.7)	0.0
Proceeds from issuance of debt			0.0	0.0
Shares repurchased			(102.2)	(41.9)
Dividends paid to common shareholders			(39.3)	(33.5)
Purchase of shares to satisfy employee tax on vested stock			(11.3)	(14.0)
Distributions to noncontrolling interest			0.0	0.0
Distributions to controlling interest in partially-owned subsidiaries			0.0	0.0
Change in intercompany financing between entities			396.8	362.0
Other			0.0	0.0
Net cash provided (required) by financing activities			(375.7)	272.6
Net increase (decrease) in cash, cash equivalents, and restricted cash			(173.1)	246.1
Cash, cash equivalents, and restricted cash at beginning of period			763.9	537.9
Cash, cash equivalents, and restricted cash at end of period	590.8	784.0	590.8	784.0
Reportable legal entities | Combined Guarantor Subsidiaries
Operating activities:
Net income	65.5	81.9	127.9	130.5
Equity in earnings of subsidiaries, net of taxes	(21.5)	(26.1)	(46.8)	(43.2)
Other			189.2	161.9
Net cash provided (required) by operating activities			270.3	249.2
Investing activities:
(Increase) decrease in short-term marketable securities			0.0	0.0
Proceeds from dispositions of property and other assets			1.8	1.0
Proceeds from railcar lease fleet sales owned more than one year			700.1	446.2
Capital expenditures – leasing			(462.3)	(268.2)
Capital expenditures – manufacturing and other			(8.7)	(7.9)
Acquisitions, net of cash acquired			0.0	0.0
(Increase) decrease in investment in partially-owned subsidiaries			4.9	11.2
Other			1.0	0.0
Net cash provided (required) by investing activities			236.8	182.3
Financing activities:
Payments to retire debt			(1.5)	(1.8)
Proceeds from issuance of debt			0.0	0.0
Shares repurchased			0.0	0.0
Dividends paid to common shareholders			0.0	0.0
Purchase of shares to satisfy employee tax on vested stock			0.0	0.0
Distributions to noncontrolling interest			0.0	0.0
Distributions to controlling interest in partially-owned subsidiaries			0.0	0.0
Change in intercompany financing between entities			(504.5)	(428.3)
Other			0.0	0.0
Net cash provided (required) by financing activities			(506.0)	(430.1)
Net increase (decrease) in cash, cash equivalents, and restricted cash			1.1	1.4
Cash, cash equivalents, and restricted cash at beginning of period			1.6	5.2
Cash, cash equivalents, and restricted cash at end of period	2.7	6.6	2.7	6.6
Reportable legal entities | Combined Non-Guarantor Subsidiaries
Operating activities:
Net income	41.3	29.6	79.7	58.2
Equity in earnings of subsidiaries, net of taxes	0.0	0.0	0.0	0.0
Other			90.8	88.5
Net cash provided (required) by operating activities			170.5	146.7
Investing activities:
(Increase) decrease in short-term marketable securities			0.0	0.0
Proceeds from dispositions of property and other assets			3.6	5.0
Proceeds from railcar lease fleet sales owned more than one year			4.0	9.6
Capital expenditures – leasing			(688.6)	(366.8)
Capital expenditures – manufacturing and other			(22.6)	(30.5)
Acquisitions, net of cash acquired			(25.0)	(5.3)
(Increase) decrease in investment in partially-owned subsidiaries			0.0	0.0
Other			0.3	(2.1)
Net cash provided (required) by investing activities			(728.3)	(390.1)
Financing activities:
Payments to retire debt			(53.4)	(96.5)
Proceeds from issuance of debt			478.0	299.4
Shares repurchased			0.0	0.0
Dividends paid to common shareholders			0.0	0.0
Purchase of shares to satisfy employee tax on vested stock			0.0	0.0
Distributions to noncontrolling interest			(10.3)	(16.9)
Distributions to controlling interest in partially-owned subsidiaries			4.9	(11.2)
Change in intercompany financing between entities			94.8	83.2
Other			(3.1)	(0.1)
Net cash provided (required) by financing activities			510.9	257.9
Net increase (decrease) in cash, cash equivalents, and restricted cash			(46.9)	14.5
Cash, cash equivalents, and restricted cash at beginning of period			208.3	198.4
Cash, cash equivalents, and restricted cash at end of period	161.4	212.9	161.4	212.9
Eliminations
Operating activities:
Net income	(105.4)	(108.6)	(204.8)	(180.1)
Equity in earnings of subsidiaries, net of taxes	118.9	129.2	228.4	205.5
Other			(26.7)	(8.6)
Net cash provided (required) by operating activities			(3.1)	16.8
Investing activities:
(Increase) decrease in short-term marketable securities			0.0	0.0
Proceeds from dispositions of property and other assets			0.0	0.0
Proceeds from railcar lease fleet sales owned more than one year			(647.7)	(363.4)
Capital expenditures – leasing			647.7	363.4
Capital expenditures – manufacturing and other			0.0	0.0
Acquisitions, net of cash acquired			0.0	0.0
(Increase) decrease in investment in partially-owned subsidiaries			(4.9)	(11.2)
Other			0.0	0.0
Net cash provided (required) by investing activities			(4.9)	(11.2)
Financing activities:
Payments to retire debt			0.0	0.0
Proceeds from issuance of debt			0.0	0.0
Shares repurchased			0.0	0.0
Dividends paid to common shareholders			0.0	0.0
Purchase of shares to satisfy employee tax on vested stock			0.0	0.0
Distributions to noncontrolling interest			0.0	0.0
Distributions to controlling interest in partially-owned subsidiaries			(4.9)	11.2
Change in intercompany financing between entities			12.9	(16.9)
Other			0.0	0.0
Net cash provided (required) by financing activities			8.0	(5.7)
Net increase (decrease) in cash, cash equivalents, and restricted cash			0.0	(0.1)
Cash, cash equivalents, and restricted cash at beginning of period			0.0	0.1
Cash, cash equivalents, and restricted cash at end of period	$ 0.0	$ 0.0	$ 0.0	$ 0.0