Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020		Sep. 30, 2019
Noncontrolling Interest [Line Items]
Balance at beginning of year	$ 541.9
Acquisition		$ 39.1		$ 194.8
Business divestiture		16.7
Net income	94.1	48.6		6.2
Net subscriptions (distributions) and other	213.6	164.4		103.6
Net deconsolidations	(552.4)	(6.8)		24.3
Adjustment to fair value	(159.2)
Balance at End of Year	933.0	541.9
Minority Interests [Member]
Noncontrolling Interest [Line Items]
Balance at beginning of year	144.6	0.0
Acquisition	0.0	164.3
Business divestiture	0.0	(21.3)
Net income	30.3	3.6
Net subscriptions (distributions) and other	(23.6)	(2.0)
Net deconsolidations	0.0	0.0
Adjustment to fair value	159.2
Balance at End of Year	310.5	144.6		0.0
Redeemable Noncontrolling Interest [Member]
Noncontrolling Interest [Line Items]
Balance at beginning of year	541.9	746.7	[1]	1,043.6	[1]
Acquisition	0.0	186.4		0.0	[1]
Business divestiture	0.0	(21.3)		0.0	[1]
Net income	94.1	48.6		6.2	[1]
Net subscriptions (distributions) and other	507.8	245.1		1,046.6	[1]
Net deconsolidations	(370.0)	(663.6)		(1,349.7)	[1]
Adjustment to fair value	159.2
Balance at End of Year	933.0	541.9		746.7	[1]
Consolidated Investment Products [Member]
Noncontrolling Interest [Line Items]
Balance at beginning of year	397.3	746.7
Acquisition	0.0	22.1
Business divestiture	0.0	0.0
Net income	63.8	45.0
Net subscriptions (distributions) and other	531.4	247.1
Net deconsolidations	(370.0)	(663.6)
Balance at End of Year	$ 622.5	$ 397.3		$ 746.7

[1] Represents redeemable noncontrolling interests of CIPs.