Deferred Acquisition Costs and Other Actuarial Balances - Retirement and Income Solutions - Balances and changes in DAC (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	$ 4,006.9
Ending balance, Deferred acquisition costs	4,048.0	$ 4,006.9
Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	957.2
Ending balance, Deferred acquisition costs	986.2	957.2
Workplace savings and retirement solutions \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	515.5	506.4
Costs deferred	25.4	47.7
Amortized to expense	(18.7)	(38.6)
Ending balance, Deferred acquisition costs	522.2	515.5
Individual variable annuities \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	323.4	279.5
Costs deferred	46.9	72.7
Amortized to expense	(16.8)	(28.8)
Ending balance, Deferred acquisition costs	353.5	323.4
Pension risk transfer \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	21.1	15.4
Costs deferred	2.7	6.6
Amortized to expense	(0.6)	(0.9)
Ending balance, Deferred acquisition costs	23.2	21.1
Individual fixed deferred annuities \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	84.2	106.1
Amortized to expense	(8.5)	(21.9)
Ending balance, Deferred acquisition costs	75.7	84.2
Investment only \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	13.0	11.5
Costs deferred	1.1	6.5
Amortized to expense	(2.5)	(5.0)
Ending balance, Deferred acquisition costs	$ 11.6	$ 13.0