Consolidated Investment Products - Schedule of Valuation Techniques and Significant Unobservable Inputs used in Level 3 Fair Value Measurements (Details) $ in Millions		Sep. 30, 2025 USD ($) $ / shares	Sep. 30, 2024 USD ($) $ / shares
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		$ 1,179.5	$ 838.0
CIPs [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		12,278.8	11,034.9
Fair Value, Recurring [Member] | CIPs [Member] | Equity and debt securities [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		1,914.8	1,856.3
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		601.0	550.1
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market pricing [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		$ 302.0	$ 214.5
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market pricing [Member] | Private sale pricing [Member] | Minimum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input | $ / shares		0.27	0.01
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market pricing [Member] | Private sale pricing [Member] | Maximum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input | $ / shares		2,120	1,000
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market pricing [Member] | Private sale pricing [Member] | Weighted Average [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input | $ / shares	[1]	176.53	73.04
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market pricing [Member] | Discount for lack of marketability [Member] | Minimum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.050	0.098
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market pricing [Member] | Discount for lack of marketability [Member] | Maximum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.750	0.175
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market pricing [Member] | Discount for lack of marketability [Member] | Weighted Average [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.239	0.115
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market comparable companies [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		$ 225.9	$ 291.6
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market comparable companies [Member] | Discount for lack of marketability [Member] | Minimum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.060	0.001
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market comparable companies [Member] | Discount for lack of marketability [Member] | Maximum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.110	0.104
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market comparable companies [Member] | Discount for lack of marketability [Member] | Weighted Average [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.085	0.081
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market comparable companies [Member] | Revenue multiple [Member] | Minimum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		1.4	1.2
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market comparable companies [Member] | Revenue multiple [Member] | Maximum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		21.0	22.8
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Market comparable companies [Member] | Revenue multiple [Member] | Weighted Average [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		9.5	10.9
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation, Income Approach [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		$ 54.4	$ 44.0
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation, Income Approach [Member] | Discount rate [Member] | Minimum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.065
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation, Income Approach [Member] | Discount rate [Member] | Maximum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.130
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation, Income Approach [Member] | Discount rate [Member] | Weighted Average [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.068	0.068
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation Technique, Option Pricing Model
Schedule Of Consolidated Investment Products [Line Items]
Investments, at fair value		$ 18.7
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation Technique, Option Pricing Model | Discount for lack of marketability [Member] | Minimum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.091
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation Technique, Option Pricing Model | Discount for lack of marketability [Member] | Maximum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.135
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation Technique, Option Pricing Model | Discount for lack of marketability [Member] | Weighted Average [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.094
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation Technique, Option Pricing Model | Measurement Input, Option Volatility | Minimum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.340
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation Technique, Option Pricing Model | Measurement Input, Option Volatility | Maximum [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.609
Fair Value, Recurring [Member] | CIPs [Member] | Level 3 [Member] | Equity and debt securities [Member] | Valuation Technique, Option Pricing Model | Measurement Input, Option Volatility | Weighted Average [Member]
Schedule Of Consolidated Investment Products [Line Items]
Investments, measurement input		0.382

[1] Based on the relative fair value of the instruments.