Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss [Member]	Accumulated Other Comprehensive Loss [Member] Cumulative Effect, Period of Adoption, Adjustment	Stockholders' Equity [Member]	Stockholders' Equity [Member] Cumulative Effect, Period of Adoption, Adjustment	Nonredeemable Noncontrolling Interests [Member]
Beginning balance - Shares at Sep. 30, 2018			519.1
Beginning balance at Sep. 30, 2018			$ 51.9	$ 0.0	$ 10,217.9		$ (370.6)		$ 9,899.2
Beginning balance (ASU 2014-09 and 2016-01 [Member]) at Sep. 30, 2018						$ 22.9		$ (8.0)		$ 14.9
Beginning balance at Sep. 30, 2018											$ 308.7
Beginning balance at Sep. 30, 2018	$ 10,207.9
Beginning balance (ASU 2014-09 and 2016-01 [Member]) at Sep. 30, 2018		$ 14.9
Stockholders' Equity [Roll Forward]
Net income	1,195.7				1,195.7				1,195.7
Nonredeemable noncontrolling interests	3.6										3.6
Net income	1,199.3
Other comprehensive income (loss)	(53.0)						(53.0)		(53.0)
Dividends declared on common stock	(528.3)				(528.3)				(528.3)
Repurchase of common stock - Shares			(24.6)
Repurchase of common stock - Amount	(756.3)		$ (2.5)	(133.8)	(620.0)				(756.3)
Issuance of common stock - Shares			4.8
Issuance of common stock - Amount	130.3		$ 0.5	129.8					130.3
Stock-based compensation	4.0			4.0					4.0
Net subscriptions and other	103.6										103.6
Net consolidation (deconsolidation) of investment products	24.3										24.3
Acquisitions	194.8										194.8
Ending balance - Shares at Sep. 30, 2019			499.3
Ending balance at Sep. 30, 2019			$ 49.9	0.0	10,288.2		(431.6)		9,906.5
Ending balance at Sep. 30, 2019											635.0
Ending balance at Sep. 30, 2019	10,541.5
Stockholders' Equity [Roll Forward]
Net income	798.9				798.9				798.9
Nonredeemable noncontrolling interests	(60.4)										(60.4)
Net income	738.5
Other comprehensive income (loss)	24.0						24.0		24.0
Dividends declared on common stock	(539.0)				(539.0)				(539.0)
Repurchase of common stock - Shares			(9.0)
Repurchase of common stock - Amount	(219.4)		$ (0.9)	(143.0)	(75.5)				(219.4)
Issuance of common stock - Shares			4.8
Issuance of common stock - Amount	127.2		$ 0.5	126.7					127.2
Stock-based compensation	16.3			16.3					16.3
Net subscriptions and other	164.4										164.4
Net consolidation (deconsolidation) of investment products	(6.8)										(6.8)
Acquisitions	39.1										39.1
Wind-down of a subsidiary	(16.7)										(16.7)
Ending balance - Shares at Sep. 30, 2020			495.1
Ending balance at Sep. 30, 2020	10,114.5		$ 49.5	0.0	10,472.6		(407.6)		10,114.5
Ending balance (ASU 2016-13 [Member]) at Sep. 30, 2020						$ (3.3)				$ (3.3)
Ending balance at Sep. 30, 2020	754.6										754.6
Ending balance at Sep. 30, 2020	10,869.1
Ending balance (ASU 2016-13 [Member]) at Sep. 30, 2020		$ (3.3)
Stockholders' Equity [Roll Forward]
Net income	1,831.2				1,831.2				1,831.2
Nonredeemable noncontrolling interests	169.3										169.3
Net income	2,000.5
Other comprehensive income (loss)	30.0						30.0		30.0
Dividends declared on common stock	(573.7)				(573.7)				(573.7)
Repurchase of common stock - Shares			(7.3)
Repurchase of common stock - Amount	(208.2)		$ (0.7)	(192.8)	(14.7)				(208.2)
Issuance of common stock - Shares			14.0
Issuance of common stock - Amount	133.4		$ 1.4	132.0					133.4
Stock-based compensation	60.8			60.8					60.8
Net subscriptions and other	213.6				(2.1)				(2.1)		215.7
Net consolidation (deconsolidation) of investment products	(552.4)										(552.4)
Adjustment to fair value of redeemable noncontrolling interests	(159.2)				(159.2)				(159.2)
Ending balance - Shares at Sep. 30, 2021			501.8
Ending balance at Sep. 30, 2021	11,223.4		$ 50.2	$ 0.0	$ 11,550.8		$ (377.6)		$ 11,223.4
Ending balance at Sep. 30, 2021	587.2										$ 587.2
Ending balance at Sep. 30, 2021	$ 11,810.6