Separate Account Balances - Benefits and Protection (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Changes in separate account liabilities
Balance at beginning of period	$ 155,375.1
Balance at end of period	162,000.8	$ 155,375.1
Benefits and Protection | Life Insurance | Universal life
Changes in separate account liabilities
Balance at beginning of period	5,011.0	5,886.1
Premiums and deposits	126.5	514.7
Policy charges	(31.9)	(122.1)
Surrenders, withdrawals and benefit payments	(115.7)	(208.6)
Investment performance	262.0	(1,054.5)
Net transfers (to) from general account	2.3	(4.6)
Balance at end of period	5,254.2	5,011.0
Cash surrender value	$ 5,308.6	$ 5,055.8