Deferred Acquisition Costs and Other Actuarial Balances - Disaggregated DAC amounts (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024	Dec. 31, 2023
Deferred Acquisition Costs
Deferred acquisition costs	$ 4,048.0	$ 4,006.9
Short-duration contracts
Deferred Acquisition Costs
Deferred acquisition costs	36.6	30.6
Other balances
Deferred Acquisition Costs
Deferred acquisition costs	5.9	5.9
Retirement and Income Solutions
Deferred Acquisition Costs
Deferred acquisition costs	986.2	957.2
Retirement and Income Solutions \| Workplace savings and retirement solutions
Deferred Acquisition Costs
Deferred acquisition costs	522.2	515.5	$ 506.4
Retirement and Income Solutions \| Individual variable annuities
Deferred Acquisition Costs
Deferred acquisition costs	353.5	323.4	279.5
Retirement and Income Solutions \| Pension risk transfer
Deferred Acquisition Costs
Deferred acquisition costs	23.2	21.1	15.4
Retirement and Income Solutions \| Individual fixed deferred annuities
Deferred Acquisition Costs
Deferred acquisition costs	75.7	84.2	106.1
Retirement and Income Solutions \| Investment only
Deferred Acquisition Costs
Deferred acquisition costs	11.6	13.0	11.5
Benefits and Protection
Deferred Acquisition Costs
Deferred acquisition costs	3,019.3	3,013.2
Benefits and Protection \| Life Insurance \| Universal life
Deferred Acquisition Costs
Deferred acquisition costs excluding short-duration contracts and other balances	1,523.6	1,527.7	1,545.3
Benefits and Protection \| Life Insurance \| Term life
Deferred Acquisition Costs
Deferred acquisition costs excluding short-duration contracts and other balances	716.1	710.8	695.1
Benefits and Protection \| Life Insurance \| Participating life
Deferred Acquisition Costs
Deferred acquisition costs excluding short-duration contracts and other balances	74.4	77.8	84.7
Benefits and Protection \| Specialty Benefits \| Individual disability
Deferred Acquisition Costs
Deferred acquisition costs excluding short-duration contracts and other balances	$ 705.2	$ 696.9	$ 667.7