Deferred Acquisition Costs and Other Actuarial Balances - Retirement and Income Solutions - Balances and changes in DAC (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	$ 3,948.0		$ 3,822.3
Ending balance, Deferred acquisition costs	3,948.4	$ 3,948.0
Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	930.0		964.4
Ending balance, Deferred acquisition costs	920.5	930.0
Workplace savings and retirement solutions | Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	498.0	489.0	477.2
Costs deferred	35.7	48.3	50.1
Amortized to expense	(29.6)	(39.3)	(38.3)
Ending balance, Deferred acquisition costs	504.1	498.0	489.0
Individual variable annuities | Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	278.0	281.2	281.9
Costs deferred	19.1	22.5	26.4
Amortized to expense	(19.4)	(25.7)	(27.1)
Ending balance, Deferred acquisition costs	277.7	278.0	281.2
Pension risk transfer | Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	8.1	2.7
Costs deferred	6.1	5.6	2.7
Amortized to expense	(0.4)	(0.2)
Ending balance, Deferred acquisition costs	13.8	8.1	2.7
Individual fixed deferred annuities | Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	131.0	162.2	192.7
Costs deferred			7.6
Amortized to expense	(18.8)	(31.2)	(38.1)
Ending balance, Deferred acquisition costs	112.2	131.0	162.2
Investment only | Retirement and Income Solutions
Deferred Acquisition Costs
Beginning balance, Deferred acquisition costs	14.9	18.1	12.6
Costs deferred	1.4	1.4	9.1
Amortized to expense	(3.6)	(4.6)	(3.6)
Ending balance, Deferred acquisition costs	$ 12.7	$ 14.9	$ 18.1