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, 2026	Dec. 31, 2025
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	$ 4,071.6
Ending balance, Deferred acquisition costs	4,102.1	$ 4,071.6
Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	1,016.5
Ending balance, Deferred acquisition costs	1,035.0	1,016.5
Workplace savings and retirement solutions \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	528.9	515.5
Costs deferred	22.2	50.9
Amortized to expense	(19.1)	(37.5)
Ending balance, Deferred acquisition costs	532.0	528.9
Individual variable annuities \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	385.3	323.4
Costs deferred	40.2	96.9
Amortized to expense	(19.5)	(35.0)
Ending balance, Deferred acquisition costs	406.0	385.3
Pension risk transfer \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	24.8	21.1
Costs deferred	2.0	5.0
Amortized to expense	(0.7)	(1.3)
Ending balance, Deferred acquisition costs	26.1	24.8
Individual fixed deferred annuities \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	66.9	84.2
Amortized to expense	(8.1)	(17.3)
Ending balance, Deferred acquisition costs	58.8	66.9
Investment only \| Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	10.6	13.0
Costs deferred	4.0	2.6
Amortized to expense	(2.5)	(5.0)
Ending balance, Deferred acquisition costs	$ 12.1	$ 10.6