Financial Statements for Guarantors of the Senior Notes - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net income	$ 28.3	$ 67.9	$ 135.4	$ 173.6
Equity in earnings of subsidiaries, net of taxes	0.0	0.0	0.0	0.0
Other			184.5	314.6
Net cash provided (required) by operating activities			319.9	488.2
Investing activities:
(Increase) decrease in short-term marketable securities			319.5	84.7
Proceeds from dispositions of property and other assets			11.8	8.1
Proceeds from railcar lease fleet sales owned more than one year			123.4	160.3
Capital expenditures – leasing			(675.8)	(360.4)
Capital expenditures – manufacturing and other			(63.0)	(61.9)
Acquisitions, net of cash acquired	0.0	(42.2)	(25.0)	(47.5)
(Increase) decrease in investment in partially-owned subsidiaries			0.0	0.0
Other			(1.9)	(0.3)
Net cash provided (required) by investing activities			(311.0)	(217.0)
Financing activities:
Payments to retire debt			(739.0)	(334.9)
Proceeds from issuance of debt, net of debt issuance costs			561.3	534.1
Shares repurchased			(156.1)	(52.4)
Dividends paid to common shareholders			(58.1)	(53.0)
Purchase of shares to satisfy employee tax on vested stock			(11.5)	(14.1)
Distributions to noncontrolling interest			(10.3)	(41.4)
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			(416.8)	38.2
Net increase (decrease) in cash, cash equivalents, and restricted cash			(407.9)	309.4
Cash, cash equivalents, and restricted cash at beginning of period			973.8	741.6
Cash, cash equivalents, and restricted cash at end of period	565.9	1,051.0	565.9	1,051.0
Reportable legal entities | Parent
Operating activities:
Net income	27.7	66.9	132.0	164.0
Equity in earnings of subsidiaries, net of taxes	(62.8)	(111.7)	(244.3)	(274.1)
Other			(24.1)	28.5
Net cash provided (required) by operating activities			(136.4)	(81.6)
Investing activities:
(Increase) decrease in short-term marketable securities			319.5	84.7
Proceeds from dispositions of property and other assets			0.2	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			(11.6)	(5.9)
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			308.1	78.8
Financing activities:
Payments to retire debt			(647.6)	0.0
Proceeds from issuance of debt, net of debt issuance costs			0.0	0.0
Shares repurchased			(156.1)	(52.4)
Dividends paid to common shareholders			(58.1)	(53.0)
Purchase of shares to satisfy employee tax on vested stock			(11.5)	(14.1)
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			270.7	437.4
Other			0.0	0.0
Net cash provided (required) by financing activities			(602.6)	317.9
Net increase (decrease) in cash, cash equivalents, and restricted cash			(430.9)	315.1
Cash, cash equivalents, and restricted cash at beginning of period			763.9	537.9
Cash, cash equivalents, and restricted cash at end of period	333.0	853.0	333.0	853.0
Reportable legal entities | Combined Guarantor Subsidiaries
Operating activities:
Net income	57.4	85.1	185.3	215.6
Equity in earnings of subsidiaries, net of taxes	(16.4)	(17.5)	(63.3)	(60.6)
Other			88.1	134.9
Net cash provided (required) by operating activities			210.1	289.9
Investing activities:
(Increase) decrease in short-term marketable securities			0.0	0.0
Proceeds from dispositions of property and other assets			2.5	1.2
Proceeds from railcar lease fleet sales owned more than one year			707.8	515.8
Capital expenditures – leasing			(611.9)	(349.2)
Capital expenditures – manufacturing and other			(14.7)	(12.3)
Acquisitions, net of cash acquired			0.0	0.0
(Increase) decrease in investment in partially-owned subsidiaries			7.1	30.0
Other			(1.9)	0.0
Net cash provided (required) by investing activities			88.9	185.5
Financing activities:
Payments to retire debt			(1.8)	(2.7)
Proceeds from issuance of debt, net of debt issuance costs			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			(228.6)	(471.8)
Other			0.0	0.0
Net cash provided (required) by financing activities			(230.4)	(474.5)
Net increase (decrease) in cash, cash equivalents, and restricted cash			68.6	0.9
Cash, cash equivalents, and restricted cash at beginning of period			1.6	5.2
Cash, cash equivalents, and restricted cash at end of period	70.2	6.1	70.2	6.1
Reportable legal entities | Combined Non-Guarantor Subsidiaries
Operating activities:
Net income	17.2	37.0	97.0	95.2
Equity in earnings of subsidiaries, net of taxes	0.0	0.0	0.0	0.0
Other			151.7	165.7
Net cash provided (required) by operating activities			248.7	260.9
Investing activities:
(Increase) decrease in short-term marketable securities			0.0	0.0
Proceeds from dispositions of property and other assets			9.1	6.9
Proceeds from railcar lease fleet sales owned more than one year			63.3	8.4
Capital expenditures – leasing			(711.6)	(375.1)
Capital expenditures – manufacturing and other			(36.7)	(43.7)
Acquisitions, net of cash acquired			(25.0)	(47.5)
(Increase) decrease in investment in partially-owned subsidiaries			0.0	0.0
Other			0.0	(0.3)
Net cash provided (required) by investing activities			(700.9)	(451.3)
Financing activities:
Payments to retire debt			(89.6)	(332.2)
Proceeds from issuance of debt, net of debt issuance costs			561.3	534.1
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)	(41.4)
Distributions to controlling interest in partially-owned subsidiaries			7.1	(30.0)
Change in intercompany financing between entities			(58.8)	53.5
Other			(3.1)	(0.1)
Net cash provided (required) by financing activities			406.6	183.9
Net increase (decrease) in cash, cash equivalents, and restricted cash			(45.6)	(6.5)
Cash, cash equivalents, and restricted cash at beginning of period			208.3	198.4
Cash, cash equivalents, and restricted cash at end of period	162.7	191.9	162.7	191.9
Eliminations
Operating activities:
Net income	(74.0)	(121.1)	(278.9)	(301.2)
Equity in earnings of subsidiaries, net of taxes	79.2	129.2	307.6	334.7
Other			(31.2)	(14.5)
Net cash provided (required) by operating activities			(2.5)	19.0
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)	(363.9)
Capital expenditures – leasing			647.7	363.9
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			(7.1)	(30.0)
Other			0.0	0.0
Net cash provided (required) by investing activities			(7.1)	(30.0)
Financing activities:
Payments to retire debt			0.0	0.0
Proceeds from issuance of debt, net of debt issuance costs			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			(7.1)	30.0
Change in intercompany financing between entities			16.7	(19.1)
Other			0.0	0.0
Net cash provided (required) by financing activities			9.6	10.9
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