Goodwill and Acquired Client Relationships - Additional Information (Details)	3 Months Ended			12 Months Ended
	Dec. 31, 2025 USD ($)	Mar. 31, 2025 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2025 USD ($)	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Intangible assets
Goodwill impairment					$ 0
Estimated Future Amortization Expense of Finite-Lived Intangibles
Long-term revenue growth rates	0.00%	0.00%		0.00%
Discount rates	10.50%	11.00%		10.50%
Cash received in Veritable Transaction			$ 287,400,000
Affiliate transaction gains			$ 133,100,000	$ 371,300,000		$ 0	$ 133,100,000
Third Party
Estimated Future Amortization Expense of Finite-Lived Intangibles
Subsidiary, ownership percentage, sold			1
Minimum
Estimated Future Amortization Expense of Finite-Lived Intangibles
Revenue growth rates	(34.00%)	(21.00%)		(34.00%)
Maximum
Estimated Future Amortization Expense of Finite-Lived Intangibles
Revenue growth rates	0.00%	0.00%		0.00%
Acquired Client Relationships
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible impairments				$ 135,000,000.0
Indefinite-lived acquired client relationships	$ 1,484,300,000			1,484,300,000		1,597,500,000	1,603,100,000
Acquired Client Relationships For Certain Mutual Fund Assets
Estimated Future Amortization Expense of Finite-Lived Intangibles
Impairment, Intangible Asset, Indefinite-Lived (Excluding Goodwill), Statement of Income or Comprehensive Income [Extensible Enumeration]	Intangible amortization and impairments	Intangible amortization and impairments
Intangible amortization and impairments attributable to controlling interest	$ 37,000,000	$ 59,200,000
Intangible impairments	58,000,000	70,000,000
Acquired Client Relationships, Mutual Fund Product
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible amortization and impairments attributable to controlling interest		4,000,000
Intangible impairments		7,000,000
Indefinite-lived acquired client relationships		$ 0
Acquired Client Relationships
Intangible assets
Amortization and impairment expenses of intangible assets				25,300,000		$ 29,000,000.0	$ 48,300,000
Estimated Future Amortization Expense of Finite-Lived Intangibles
Intangible future amortization expense in 2026	25,000,000			25,000,000
Intangible future amortization expense in 2027	25,000,000			25,000,000
Intangible future amortization expense in 2028	25,000,000			25,000,000
Intangible future amortization expense in 2029	15,000,000			15,000,000
Intangible future amortization expense in 2030	$ 10,000,000			10,000,000
Impairment of definite-lived intangible assets				$ 0