Deferred Acquisition Costs and Other Actuarial Balances - Disaggregated DAC amounts (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Deferred Acquisition Costs
Deferred acquisition costs	$ 4,006.9	$ 3,950.5
Short-duration contracts
Deferred Acquisition Costs
Deferred acquisition costs	30.6	31.1
Other balances
Deferred Acquisition Costs
Deferred acquisition costs	5.9	7.7
Retirement and Income Solutions
Deferred Acquisition Costs
Deferred acquisition costs	957.2	918.9
Retirement and Income Solutions \| Workplace savings and retirement solutions
Deferred Acquisition Costs
Deferred acquisition costs	515.5	506.4	$ 498.0
Retirement and Income Solutions \| Individual variable annuities
Deferred Acquisition Costs
Deferred acquisition costs	323.4	279.5	278.0
Retirement and Income Solutions \| Pension risk transfer
Deferred Acquisition Costs
Deferred acquisition costs	21.1	15.4	8.1
Retirement and Income Solutions \| Individual fixed deferred annuities
Deferred Acquisition Costs
Deferred acquisition costs	84.2	106.1	131.0
Retirement and Income Solutions \| Investment only
Deferred Acquisition Costs
Deferred acquisition costs	13.0	11.5	14.9
Benefits and Protection
Deferred Acquisition Costs
Deferred acquisition costs	3,043.8	3,023.9
Deferred acquisition costs excluding short-duration contracts and other balances	3,013.2	2,992.8
Benefits and Protection \| Specialty Benefits \| Individual disability
Deferred Acquisition Costs
Deferred acquisition costs	696.9	667.7	626.1
Deferred acquisition costs excluding short-duration contracts and other balances	696.9	667.7
Benefits and Protection \| Life Insurance \| Universal life
Deferred Acquisition Costs
Deferred acquisition costs	1,527.7	1,545.3	1,569.7
Deferred acquisition costs excluding short-duration contracts and other balances	1,527.7	1,545.3
Benefits and Protection \| Life Insurance \| Term life
Deferred Acquisition Costs
Deferred acquisition costs	710.8	695.1	685.7
Deferred acquisition costs excluding short-duration contracts and other balances	710.8	695.1
Benefits and Protection \| Life Insurance \| Participating life
Deferred Acquisition Costs
Deferred acquisition costs	77.8	84.7	$ 93.0
Deferred acquisition costs excluding short-duration contracts and other balances	$ 77.8	$ 84.7