Business and Basis of Presentation (Unearned Revenue Reserves) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance prior to transition	$ 13,198,477	$ 12,664,445	$ 12,093,263	$ 11,660,527
Unwinding amounts related to unrealized investment gains and losses and other activity		$ (12,611)		$ (215,658)
Less: Reinsurance recoverables	12,979,687		11,902,756
Balance after transition, net of reinsurance recoverable	$ 218,790		$ 190,507
Variable/Universal Life | Policyholder Contract Deposit
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance prior to transition					$ 1,745,268
Less: Reinsurance recoverables					751,517
Balance after transition, net of reinsurance recoverable					993,751
Variable/Universal Life | As Previously Reported | Policyholder Contract Deposit
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Balance prior to transition						$ 1,377,669
Variable/Universal Life | Changes in benefit reserves | Policyholder Contract Deposit
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Unwinding amounts related to unrealized investment gains and losses and other activity					$ 367,599