Deferred Acquisition Costs and Other Actuarial Balances - Unearned Revenue Liability (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other Actuarial Balances
Total unearned revenue liability	$ 486.9	$ 467.4
Benefits and Protection | Life Insurance
Other Actuarial Balances
Total unearned revenue liability				$ 384.4
Universal life | Benefits and Protection | Life Insurance
Other Actuarial Balances
Total unearned revenue liability	479.7	459.0	$ 425.3	$ 384.4
Other balances
Other Actuarial Balances
Total unearned revenue liability	$ 7.2	$ 8.4