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	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	$ 6,107	$ 5,685
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	5,996	5,582
Short-term FHLB borrowings outstanding	225	265
Notes	24,895	23,786
Convertible debentures		63
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	5,972	5,558
Short-term FHLB borrowings outstanding	225	265
Notes	23,569	21,861
Convertible debentures		463
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
Short-term FHLB borrowings outstanding	0	0
Notes	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
Short-term FHLB borrowings outstanding	225	265
Notes	23,569	21,861
Convertible debentures		463
Fair Value, Recurring [Member] | Level III [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	5,972	5,558
Short-term FHLB borrowings outstanding	0	0
Notes	$ 0	0
Convertible debentures		$ 0