Condensed Consolidated Statements of Shareholders' Equity (unaudited) Statement - USD ($)	Total	Previously Reported	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock [Member]
Common Stock, Shares, Outstanding, Beginning Balance at Sep. 30, 2019			88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Sep. 30, 2019	$ 1,573,300,000		$ 4,400,000			$ (182,500,000)	$ (853,400,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Standard Adjustment | Accounting Standards Update 2016-13 [Member]					$ 100,000
Net Income (Loss) Attributable to Parent	180,600,000				180,600,000
Other Comprehensive Income (Loss), Net of Tax	(29,700,000)					(29,700,000)
Dividends	(43,300,000)			$ 400,000	(43,700,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(16,400,000)						(16,400,000)
Payments for Repurchase of Common Stock	(54,100,000)						(54,100,000)
Share-based Payment Arrangement, Increase for Cost Recognition	26,400,000			26,400,000
Stock Issued During Period, Value, Stock Options Exercised	(8,500,000)			(2,900,000)			(5,600,000)
Stock Issued During Period, Value	0			(16,900,000)			16,900,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	6,800,000			4,200,000			2,600,000
Other Comprehensive Income (Loss), Tax						11,400,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2020	1,652,400,000		$ 4,400,000	654,400,000	2,104,600,000	(212,200,000)	(898,800,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance (Retained Earnings [Member]) at Jun. 30, 2020		$ 300,000
Common Stock, Shares, Outstanding, Beginning Balance at Sep. 30, 2019			88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Sep. 30, 2019	1,573,300,000		$ 4,400,000			(182,500,000)	(853,400,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	$ (29,700,000)
Common Stock, Dividends, Per Share, Cash Paid	$ 0.65
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Sep. 30, 2020	$ 1,726,100,000		$ 4,400,000	667,000,000.0	2,132,200,000	(180,200,000)	(897,300,000)
Common Stock, Shares, Outstanding, Beginning Balance at Mar. 31, 2020			88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Mar. 31, 2020	1,548,900,000		$ 4,400,000	644,400,000	2,025,200,000	(223,600,000)	(901,500,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
New Accounting Standard Adjustment | Accounting Standards Update 2016-13 [Member]					800,000
Net Income (Loss) Attributable to Parent	93,900,000				93,900,000
Other Comprehensive Income (Loss), Net of Tax	11,400,000					11,400,000
Dividends	(14,600,000)			200,000	(14,800,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(600,000)						(600,000)
Share-based Payment Arrangement, Increase for Cost Recognition	7,900,000			7,900,000
Stock Issued During Period, Value, Stock Options Exercised	(2,800,000)			(1,200,000)			(1,600,000)
Stock Issued During Period, Value	(100,000)			(800,000)			700,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	2,500,000			1,500,000			1,000,000.0
Other Comprehensive Income (Loss), Tax						1,600,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2020	$ 1,652,400,000		$ 4,400,000	654,400,000	2,104,600,000	(212,200,000)	(898,800,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance (Retained Earnings [Member]) at Jun. 30, 2020		300,000
Common Stock, Shares, Outstanding, Beginning Balance at Jun. 30, 2020			88,457,634
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.22
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Sep. 30, 2020	$ 1,726,100,000		$ 4,400,000	667,000,000.0	2,132,200,000	(180,200,000)	(897,300,000)
Common Stock, Shares, Outstanding, Beginning Balance at Sep. 30, 2020	66,640,832		88,457,634
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	$ 195,100,000				195,100,000
Other Comprehensive Income (Loss), Net of Tax	40,700,000					40,700,000
Dividends	(46,300,000)			400,000	(46,700,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(9,300,000)						(9,300,000)
Payments for Repurchase of Common Stock	(130,700,000)						(130,700,000)
Share-based Payment Arrangement, Increase for Cost Recognition	32,000,000.0			32,000,000.0
Stock Issued During Period, Value, Stock Options Exercised	(8,100,000)			(2,600,000)			(5,500,000)
Stock Issued During Period, Value	0			(12,300,000)			12,300,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	7,500,000			4,500,000			3,000,000.0
Other Comprehensive Income (Loss), Tax						(4,500,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2021	$ 1,821,000,000.0	(2,200,000)	$ 4,400,000	694,200,000	2,278,400,000	(139,500,000)	(1,016,500,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance (Retained Earnings [Member]) at Jun. 30, 2021		(2,200,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-13 [Member]
Common Stock, Shares, Outstanding, Beginning Balance at Mar. 31, 2021			88,457,634
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Mar. 31, 2021	$ 1,839,700,000		$ 4,400,000	681,700,000	2,245,100,000	(153,200,000)	(938,300,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	49,200,000				49,200,000
Other Comprehensive Income (Loss), Net of Tax	13,700,000					13,700,000
Dividends	(15,800,000)			100,000	(15,900,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(800,000)						(800,000)
Payments for Repurchase of Common Stock							(83,300,000)
Share-based Payment Arrangement, Increase for Cost Recognition	9,700,000			9,700,000
Stock Issued During Period, Value, Stock Options Exercised	(6,100,000)			(2,200,000)			(3,900,000)
Stock Issued During Period, Value	0			(1,100,000)			1,100,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	2,500,000			1,600,000			900,000
Other Comprehensive Income (Loss), Tax						(800,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2021	$ 1,821,000,000.0	(2,200,000)	$ 4,400,000	$ 694,200,000	$ 2,278,400,000	$ (139,500,000)	$ (1,016,500,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance (Retained Earnings [Member]) at Jun. 30, 2021		$ (2,200,000)