Debt - Schedule of Credit and Liquidity Facilities (Details) - Revolving Credit Facility - Line of Credit - USD ($)	Sep. 30, 2025	Sep. 02, 2025	Jun. 27, 2025	Nov. 21, 2024	Jun. 30, 2023
AGM Credit Facility \| Asset Management
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 1,250,000,000			$ 1,250,000,000
Line of credit facility, maximum borrowing capacity including potential increases	1,500,000,000
Bridge Credit Facility \| Asset Management
Debt Instrument [Line Items]
Maximum borrowing capacity	150,000,000	$ 150,000,000
Line of credit facility, maximum borrowing capacity including potential increases	225,000,000
AHL Credit Facility \| Retirement Services
Debt Instrument [Line Items]
Maximum borrowing capacity	1,250,000,000				$ 1,250,000,000
Line of credit facility, maximum borrowing capacity including potential increases	1,750,000,000				$ 1,750,000,000
AHL Liquidity Facility \| Retirement Services
Debt Instrument [Line Items]
Maximum borrowing capacity	2,600,000,000		$ 2,600,000,000
Line of credit facility, maximum borrowing capacity including potential increases	$ 3,100,000,000		$ 3,100,000,000