Financial Statements for Guarantors of the Senior Notes - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net income	$ 41.6	$ 51.7
Equity in earnings of subsidiaries, net of taxes	0.0	0.0
Other	132.1	168.4
Net cash provided (required) by operating activities	173.7	220.1
Investing activities:
(Increase) decrease in short-term marketable securities	98.7	42.6
Proceeds from dispositions of property and other assets	2.5	3.6
Proceeds from railcar lease fleet sales owned more than one year	15.5	0.0
Capital expenditures – leasing	(318.2)	(162.9)
Capital expenditures – manufacturing and other	(15.8)	(24.3)
Acquisitions, net of cash acquired	(25.0)	0.0
(Increase) decrease in investment in partially-owned subsidiaries	0.0	0.0
Other	0.8	0.5
Net cash provided (required) by investing activities	(241.5)	(140.5)
Financing activities:
Payments to retire debt	(26.5)	(26.7)
Proceeds from issuance of debt	0.9	0.0
Shares repurchased	(49.3)	0.0
Dividends paid to common shareholders	(19.5)	(16.7)
Purchase of shares to satisfy employee tax on vested stock	(0.1)	0.0
Distributions to noncontrolling interest	(5.8)	(7.3)
Distributions to controlling interest in partially-owned subsidiaries	0.0	0.0
Change in intercompany financing between entities	0.0	0.0
Other	(3.0)	0.0
Net cash provided (required) by financing activities	(103.3)	(50.7)
Net increase (decrease) in cash, cash equivalents, and restricted cash	(171.1)	28.9
Cash, cash equivalents, and restricted cash at beginning of period	973.8	741.6
Cash, cash equivalents, and restricted cash at end of period	802.7	770.5
Reportable legal entities | Parent
Operating activities:
Net income	40.2	46.0
Equity in earnings of subsidiaries, net of taxes	(84.4)	(57.6)
Other	(13.5)	10.2
Net cash provided (required) by operating activities	(57.7)	(1.4)
Investing activities:
(Increase) decrease in short-term marketable securities	98.7	42.6
Proceeds from dispositions of property and other assets	0.0	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	(1.4)	(2.1)
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	97.3	40.5
Financing activities:
Payments to retire debt	0.0	0.0
Proceeds from issuance of debt	0.0	0.0
Shares repurchased	(49.3)	0.0
Dividends paid to common shareholders	(19.5)	(16.7)
Purchase of shares to satisfy employee tax on vested stock	(0.1)	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	(126.9)	2.6
Other	0.0	0.0
Net cash provided (required) by financing activities	(195.8)	(14.1)
Net increase (decrease) in cash, cash equivalents, and restricted cash	(156.2)	25.0
Cash, cash equivalents, and restricted cash at beginning of period	763.9	537.9
Cash, cash equivalents, and restricted cash at end of period	607.7	562.9
Reportable legal entities | Combined Guarantor Subsidiaries
Operating activities:
Net income	62.4	47.7
Equity in earnings of subsidiaries, net of taxes	(25.2)	(17.0)
Other	95.2	132.7
Net cash provided (required) by operating activities	132.4	163.4
Investing activities:
(Increase) decrease in short-term marketable securities	0.0	0.0
Proceeds from dispositions of property and other assets	0.7	0.6
Proceeds from railcar lease fleet sales owned more than one year	15.5	0.0
Capital expenditures – leasing	(297.2)	(161.7)
Capital expenditures – manufacturing and other	(3.6)	(6.2)
Acquisitions, net of cash acquired	0.0	0.0
(Increase) decrease in investment in partially-owned subsidiaries	3.9	4.9
Other	0.8	0.0
Net cash provided (required) by investing activities	(279.9)	(162.4)
Financing activities:
Payments to retire debt	(0.9)	(0.9)
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	154.4	(0.1)
Other	0.0	0.0
Net cash provided (required) by financing activities	153.5	(1.0)
Net increase (decrease) in cash, cash equivalents, and restricted cash	6.0	0.0
Cash, cash equivalents, and restricted cash at beginning of period	1.6	5.2
Cash, cash equivalents, and restricted cash at end of period	7.6	5.2
Reportable legal entities | Combined Non-Guarantor Subsidiaries
Operating activities:
Net income	38.5	28.4
Equity in earnings of subsidiaries, net of taxes	0.0	0.0
Other	61.1	29.3
Net cash provided (required) by operating activities	99.6	57.7
Investing activities:
(Increase) decrease in short-term marketable securities	0.0	0.0
Proceeds from dispositions of property and other assets	1.8	3.0
Proceeds from railcar lease fleet sales owned more than one year	0.0	0.0
Capital expenditures – leasing	(21.0)	(1.2)
Capital expenditures – manufacturing and other	(10.8)	(16.0)
Acquisitions, net of cash acquired	(25.0)	0.0
(Increase) decrease in investment in partially-owned subsidiaries	0.0	0.0
Other	0.0	0.5
Net cash provided (required) by investing activities	(55.0)	(13.7)
Financing activities:
Payments to retire debt	(25.6)	(25.8)
Proceeds from issuance of debt	0.9	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	(5.8)	(7.3)
Distributions to controlling interest in partially-owned subsidiaries	3.9	(4.9)
Change in intercompany financing between entities	(35.9)	(2.0)
Other	(3.0)	0.0
Net cash provided (required) by financing activities	(65.5)	(40.0)
Net increase (decrease) in cash, cash equivalents, and restricted cash	(20.9)	4.0
Cash, cash equivalents, and restricted cash at beginning of period	208.3	198.4
Cash, cash equivalents, and restricted cash at end of period	187.4	202.4
Eliminations
Operating activities:
Net income	(99.5)	(70.4)
Equity in earnings of subsidiaries, net of taxes	109.6	74.6
Other	(10.7)	(3.8)
Net cash provided (required) by operating activities	(0.6)	0.4
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	0.0	0.0
Capital expenditures – leasing	0.0	0.0
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	(3.9)	(4.9)
Other	0.0	0.0
Net cash provided (required) by investing activities	(3.9)	(4.9)
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	(3.9)	4.9
Change in intercompany financing between entities	8.4	(0.5)
Other	0.0	0.0
Net cash provided (required) by financing activities	4.5	4.4
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