Nature of Operations and Significant Accounting Policies - Balances and changes in the unearned revenue liability (Details) - Benefits and Protection - Life Insurance - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in unearned revenue liability
Beginning balance, Unearned Revenue Liability	$ 467.4		$ 384.4
Ending balance, Unearned Revenue Liability	475.4	$ 467.4
Universal life
Change in unearned revenue liability
Beginning balance, Unearned Revenue Liability	459.0	425.3	384.4
Deferrals	15.0	61.8	66.1
Revenue recognized	(7.4)	(28.1)	(25.2)
Ending balance, Unearned Revenue Liability	$ 466.6	$ 459.0	$ 425.3