10-K Investments - Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net Investment Income [Line Items]
Investment Income, Net					$ 1,528	$ 1,419	$ 915
Investment Income, Investment Expense					(43)	(41)	(38)
Net investment income	$ 493	$ 371	$ 1,296	$ 1,112	1,485	1,378	877
Fixed Maturities [Member]
Net Investment Income [Line Items]
Investment Income, Net					971	755	725
Equity Securities [Member]
Net Investment Income [Line Items]
Investment Income, Net					48	43	71
Cash and Cash Equivalents
Net Investment Income [Line Items]
Investment Income, Net					77	5	28
Other Investments [Member]
Net Investment Income [Line Items]
Investment Income, Net					$ 432	$ 616	$ 91