Nature of Operations and Significant Accounting Policies - Balances and changes in DAC (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs		$ 3,948.0		$ 3,822.3
Ending balance, Deferred acquisition costs	$ 3,949.9	3,949.9	$ 3,948.0
Retirement and Income Solutions
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs		930.0		964.4
Ending balance, Deferred acquisition costs	922.7	922.7	930.0
Benefits and Protection
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs		2,974.5		2,857.9
Ending balance, Deferred acquisition costs	2,981.5	2,981.5	2,974.5
Workplace savings and retirement solutions \| Retirement and Income Solutions
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs	501.0	498.0	489.0	477.2
Costs deferred		22.7	48.3	50.1
Amortized to expense		(19.7)	(39.3)	(38.3)
Ending balance, Deferred acquisition costs	501.0	501.0	498.0	489.0
Individual variable annuities \| Retirement and Income Solutions
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs	276.8	278.0	281.2	281.9
Costs deferred		11.7	22.5	26.4
Amortized to expense		(12.9)	(25.7)	(27.1)
Ending balance, Deferred acquisition costs	276.8	276.8	278.0	281.2
Pension risk transfer \| Retirement and Income Solutions
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs	12.7	8.1	2.7
Costs deferred		4.8	5.6	2.7
Amortized to expense		(0.2)	(0.2)
Ending balance, Deferred acquisition costs	12.7	12.7	8.1	2.7
Individual fixed deferred annuities \| Retirement and Income Solutions
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs	118.7	131.0	162.2	192.7
Costs deferred				7.6
Amortized to expense		(12.3)	(31.2)	(38.1)
Ending balance, Deferred acquisition costs	118.7	118.7	131.0	162.2
Investment only \| Retirement and Income Solutions
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs	13.5	14.9	18.1	12.6
Costs deferred		0.9	1.4	9.1
Amortized to expense		(2.3)	(4.6)	(3.6)
Ending balance, Deferred acquisition costs	13.5	13.5	14.9	18.1
Individual disability \| Benefits and Protection \| Specialty Benefits
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs		626.1	580.7	529.8
Costs deferred		42.3	87.6	89.8
Amortized to expense		(22.2)	(42.2)	(38.9)
Ending balance, Deferred acquisition costs	646.2	646.2	626.1	580.7
Universal life \| Benefits and Protection \| Life Insurance
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs		1,569.7	1,596.2	1,608.3
Costs deferred		35.7	70.6	84.3
Amortized to expense		(48.4)	(97.1)	(96.4)
Ending balance, Deferred acquisition costs	1,557.0	1,557.0	1,569.7	1,596.2
Term life \| Benefits and Protection \| Life Insurance
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs		685.7	678.9	607.9
Costs deferred		34.4	66.7	126.5
Amortized to expense		(30.6)	(59.9)	(55.5)
Ending balance, Deferred acquisition costs	689.5	689.5	685.7	678.9
Participating life \| Benefits and Protection \| Life Insurance
Change in deferred acquisition costs
Beginning balance, Deferred acquisition costs		93.0	102.3	111.9
Costs deferred		0.7	1.4	1.9
Amortized to expense		(4.9)	(10.7)	(11.5)
Ending balance, Deferred acquisition costs	$ 88.8	$ 88.8	$ 93.0	$ 102.3