10-K Fair Value (Carrying and Fair Value By Level of Financial Instruments Not Recorded At Fair Value On Consolidated Balance Sheet) (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
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	$ 6,118		$ 6,118		$ 5,685	$ 5,225
Convertible debentures					63
Gains (losses) recognized in net income	0	$ 0	(11)	$ 1	(1)	19	$ (22)
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	6,016		6,016		5,582	5,087
Short-term FHLB borrowings outstanding					265	275
Commercial paper						300
Notes	24,844		24,844		23,786	22,384
Convertible debentures					63	72
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	6,016		6,016		5,582	5,087
Short-term FHLB borrowings outstanding					265	275
Commercial paper						300
Notes	21,815		21,815		21,861	25,150
Convertible debentures					463	687
Fair Value, Recurring [Member] | Level I [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0		0		0
Short-term FHLB borrowings outstanding						0
Notes	0		0		0
Convertible debentures					0
Fair Value, Recurring [Member] | Level II [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	0		0		0	0
Short-term FHLB borrowings outstanding					265	275
Commercial paper						300
Notes	21,815		21,815		21,861	25,150
Convertible debentures					463	687
Fair Value, Recurring [Member] | Level III [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	6,016		6,016		5,582	5,087
Short-term FHLB borrowings outstanding					0	0
Commercial paper						0
Notes	$ 0		$ 0		0	0
Convertible debentures					$ 0	$ 0