10-K Investments (Narrative) (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Schedule of Investments [Line Items]
Accrued investment income receivable	$ 281		$ 281		$ 245	$ 205
Fair value of collateral received at time of securities lending transactions	$ 2,403		$ 2,403		$ 2,457	$ 2,155
Securities lending transactions ratio of fair value of collateral held to fair value of securities loaned	102.00%		102.00%		102.00%	102.00%
Fixed Maturity Securities, Allowance for Credit Loss	$ (3)		$ (3)		$ (9)	$ (6)
Number Of Fixed Maturity Investments That Did Not Produce Income					8	2
Assets Held by Insurance Regulators					$ 752	$ 632
United States Government Securities [Member]
Schedule of Investments [Line Items]
Fixed Maturity Securities, Allowance for Credit Loss	0		0
Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Fixed Maturity Securities, Allowance for Credit Loss	0		0
States, Municipalities And Political Subdivisions [Member]
Schedule of Investments [Line Items]
Fixed Maturity Securities, Allowance for Credit Loss	0		0
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Proceeds from Sale of Available-for-sale Securities	6,236	$ 5,281	21,321	$ 15,953	22,048	10,565	$ 11,122
Fixed Maturity Securities, Allowance for Credit Loss					(9)	(6)
Fixed Maturities [Member] | United States Government Securities [Member]
Schedule of Investments [Line Items]
Fixed Maturity Securities, Allowance for Credit Loss					0	0
Fixed Maturities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Fixed Maturity Securities, Allowance for Credit Loss					0	0
Fixed Maturities [Member] | States, Municipalities And Political Subdivisions [Member]
Schedule of Investments [Line Items]
Fixed Maturity Securities, Allowance for Credit Loss					0	0
Third party investments
Schedule of Investments [Line Items]
Contractual Obligation					1,504	1,558
Rated notes
Schedule of Investments [Line Items]
Contractual Obligation					185	329
Overnight and Continuous [Member] | Cash [Member]
Schedule of Investments [Line Items]
Collateral received for securities loaned, at carrying value	2,266		2,266		2,221
Overnight and Continuous [Member] | United States Government Securities [Member]
Schedule of Investments [Line Items]
Collateral received for securities loaned, at carrying value	92		92		224
Overnight and Continuous [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Collateral received for securities loaned, at carrying value	38		38		12
Overnight and Continuous [Member] | States, Municipalities And Political Subdivisions [Member]
Schedule of Investments [Line Items]
Collateral received for securities loaned, at carrying value	$ 7		$ 7		0
Overnight and Continuous [Member] | Cash [Member]
Schedule of Investments [Line Items]
Collateral received for securities loaned, at carrying value					2,221	1,874
Overnight and Continuous [Member] | United States Government Securities [Member]
Schedule of Investments [Line Items]
Collateral received for securities loaned, at carrying value					224	281
Overnight and Continuous [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Collateral received for securities loaned, at carrying value					$ 12	$ 0