Future Contract Benefits - Summary of Changes in Present Values of LFPB (Group Protection) (Details) - Group Protection - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2023
Present Value of Expected Future Policy Benefits
Balance as of beginning-of-year	$ 5,628	$ 5,689
Effect of cumulative changes in discount rate assumptions			$ (550)	$ (490)
Beginning balance at original discount rate	6,178	6,179
Effect of changes in cash flow assumptions			(66)	(2)
Effect of actual variances from expected experience			$ (191)	$ (278)
Adjusted balance as of beginning-of-year	5,921	5,899
Issuances	1,176	1,236
Interest accrual	148	138
Benefit payments	(1,080)	(1,125)
Ending balance at original discount rate	6,165	6,148
Effect of cumulative changes in discount rate assumptions	(371)	(375)
Balance as of end-of-period	5,794	5,773
Less: Reinsurance recoverables	127	120
Net balance as of end-of-period, net of reinsurance	$ 5,667	$ 5,653
Weighted-average duration of future policyholder benefit liability	5 years	5 years