Future Policy Benefit Reserves - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Insurance [Abstract]
Liability for unpaid claims and claims adjustment expense, long term care policies, period increase (decrease)	$ 8	$ 186
Insurance claims and policyholders benefits, including policyholders' dividends, remeasurement impact			$ (88)	$ (214)	$ (8)
Liability for future policy benefit, expected future gross premium, discounted, before reinsurance			$ 3,824	$ 4,070
Liability for future policy benefit, weighted-average duration			11 years	12 years
Liability future policy benefit, losses recognized in current period			$ 164	$ 178
Liability future policy benefit, losses recognized in prior period			$ 42	$ 12