Fair value measurements (Carrying Values And Fair Values Of Financial Instruments Not Measured At Fair Value) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value	$ 0	$ 8,439
Private debt held-for-investment	2,401	0
Total assets (preliminary)	222,748	199,017
Debt Securities, Held-to-maturity		8,882
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements (refer to Note 3 for balances associated with VIEs)	2,617	1,419
Short-term debt	700	475
Long-term debt	13,736	14,402
Total liabilities	165,244	148,498
Portion at Other than Fair Value Measurement | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,299
Private debt held-for-investment	0
Total assets (preliminary)	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements (refer to Note 3 for balances associated with VIEs)	0	0
Short-Term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Trust preferred securities	0	0
Total liabilities	0	0
Portion at Other than Fair Value Measurement | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		7,140
Private debt held-for-investment	0
Total assets (preliminary)	0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements (refer to Note 3 for balances associated with VIEs)	2,617	1,419
Short-Term Debt, Fair Value	688	473
Long-term Debt, Fair Value	11,627	12,495
Trust preferred securities	362	383
Total liabilities	15,294	14,770
Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Private debt held-for-investment	2,389
Total assets (preliminary)	2,389
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements (refer to Note 3 for balances associated with VIEs)	0	0
Short-Term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Trust preferred securities	0	0
Total liabilities	0	0
Portion at Other than Fair Value Measurement | Total Level 1, Level 2, and Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		8,439
Private debt held-for-investment	2,389
Total assets (preliminary)	2,389
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements (refer to Note 3 for balances associated with VIEs)	2,617	1,419
Short-Term Debt, Fair Value	688	473
Long-term Debt, Fair Value	11,627	12,495
Trust preferred securities	362	383
Total liabilities	15,294	14,770
Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Private debt held-for-investment	2,401
Total assets (preliminary)	2,401
Debt Securities, Held-to-maturity		8,848
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Repurchase agreements (refer to Note 3 for balances associated with VIEs)	2,617	1,419
Short-term debt	700	475
Long-term debt	13,736	14,402
Trust preferred securities	308	308
Total liabilities	$ 17,361	16,604
U.S. Treasury / Agency
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,370
Debt Securities, Held-to-maturity		1,417
U.S. Treasury / Agency | Portion at Other than Fair Value Measurement | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,299
U.S. Treasury / Agency | Portion at Other than Fair Value Measurement | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		71
U.S. Treasury / Agency | Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
U.S. Treasury / Agency | Portion at Other than Fair Value Measurement | Total Level 1, Level 2, and Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,370
U.S. Treasury / Agency | Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Debt Securities, Held-to-maturity		1,417
Non-U.S.
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,054
Debt Securities, Held-to-maturity		1,140
Non-U.S. | Portion at Other than Fair Value Measurement | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Non-U.S. | Portion at Other than Fair Value Measurement | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,054
Non-U.S. | Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Non-U.S. | Portion at Other than Fair Value Measurement | Total Level 1, Level 2, and Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,054
Non-U.S. | Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Debt Securities, Held-to-maturity		1,136
Corporate and asset-backed securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,580
Debt Securities, Held-to-maturity		1,733
Corporate and asset-backed securities | Portion at Other than Fair Value Measurement | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Corporate and asset-backed securities | Portion at Other than Fair Value Measurement | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,580
Corporate and asset-backed securities | Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Corporate and asset-backed securities | Portion at Other than Fair Value Measurement | Total Level 1, Level 2, and Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,580
Corporate and asset-backed securities | Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Debt Securities, Held-to-maturity		1,705
Mortgage-backed securities
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,351
Debt Securities, Held-to-maturity		1,456
Mortgage-backed securities | Portion at Other than Fair Value Measurement | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Mortgage-backed securities | Portion at Other than Fair Value Measurement | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,351
Mortgage-backed securities | Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Mortgage-backed securities | Portion at Other than Fair Value Measurement | Total Level 1, Level 2, and Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		1,351
Mortgage-backed securities | Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Debt Securities, Held-to-maturity		1,455
Municipal
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		3,084
Debt Securities, Held-to-maturity		3,136
Municipal | Portion at Other than Fair Value Measurement | Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Municipal | Portion at Other than Fair Value Measurement | Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		3,084
Municipal | Portion at Other than Fair Value Measurement | Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		0
Municipal | Portion at Other than Fair Value Measurement | Total Level 1, Level 2, and Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Fixed maturities, held-to-maturity, fair value		3,084
Municipal | Reported Value Measurement [Member]
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Debt Securities, Held-to-maturity		$ 3,135