Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2023		Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	$ 96,789		$ 85,220
Equity securities, at fair value	1,043		827
Other Short-Term Investments	4,097		4,960
Other investments, at fair value	14,707		13,696
Securities lending collateral	1,525		1,523
Separate account assets	5,574		5,190
Market risk benefits	722		800
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other investments, at fair value	13,288		12,355
Policy Loans
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other investments, at fair value	389		343
Other Investments
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other investments, at fair value	47		47
U.S. Treasury / Agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,744		2,626
Non-U.S.
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	29,702		25,908
Corporate and asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	40,177		36,955
Mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	17,972		15,851
Municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	5,194		3,880
Level 1 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,121		2,100
Equity securities, at fair value	957		737
Other Short-Term Investments	2,335		3,108
Other investments, at fair value	542	[1]	552	[2]
Securities lending collateral	0		0
Investment derivative instruments	27		82
Derivatives designated as hedging instruments	0		0
Other derivative instruments	10		33
Separate account assets	5,480		5,101
Total assets measured at fair value	12,472	[1]	11,713	[2]
Investment derivatives	158		139
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	32
Market risk benefits	0	[3]	0	[4]
Total liabilities measured at fair value	190		139
Level 1 | U.S. Treasury / Agency | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,121		2,100
Level 1 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Level 1 | Corporate and asset-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Level 1 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Level 1 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Level 2 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	90,485		80,096
Equity securities, at fair value	0		0
Other Short-Term Investments	1,759		1,849
Other investments, at fair value	441	[1]	399	[2]
Securities lending collateral	1,525		1,523
Investment derivative instruments	0		0
Derivatives designated as hedging instruments	64		17
Other derivative instruments	0		0
Separate account assets	94		89
Total assets measured at fair value	94,368	[1]	83,973	[2]
Investment derivatives	0		0
Derivatives designated as hedging instruments	47		53
Other derivative instruments, liability	4
Market risk benefits	0	[3]	0	[4]
Total liabilities measured at fair value	51		53
Level 2 | U.S. Treasury / Agency | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	623		526
Level 2 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	29,053		25,344
Level 2 | Corporate and asset-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	37,653		34,506
Level 2 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	17,962		15,840
Level 2 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	5,194		3,880
Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,183		3,024
Equity securities, at fair value	86		90
Other Short-Term Investments	3		3
Other investments, at fair value	0	[1]	0	[2]
Securities lending collateral	0		0
Investment derivative instruments	0		0
Derivatives designated as hedging instruments	0		0
Other derivative instruments	0		0
Separate account assets	0		0
Total assets measured at fair value	3,272	[1]	3,117	[2]
Investment derivatives	0		0
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	0
Market risk benefits	722	[3]	800	[4]
Total liabilities measured at fair value	722		800
Level 3 | U.S. Treasury / Agency | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Level 3 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	649		564
Level 3 | Corporate and asset-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	2,524		2,449
Level 3 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	10		11
Level 3 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	0		0
Total Level 1, Level 2, and Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	96,789		85,220
Equity securities, at fair value	1,043		827
Other Short-Term Investments	4,097		4,960
Other investments, at fair value	983	[1]	951	[2]
Securities lending collateral	1,525		1,523
Investment derivative instruments	27		82
Derivatives designated as hedging instruments	64		17
Other derivative instruments	10		33
Separate account assets	5,574		5,190
Total assets measured at fair value	110,112	[1]	98,803	[2]
Investment derivatives	158		139
Derivatives designated as hedging instruments	47		53
Other derivative instruments, liability	36
Market risk benefits	722	[3]	800	[4]
Total liabilities measured at fair value	963		992
Total Level 1, Level 2, and Level 3 | U.S. Treasury / Agency | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,744		2,626
Total Level 1, Level 2, and Level 3 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	29,702		25,908
Total Level 1, Level 2, and Level 3 | Corporate and asset-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	40,177		36,955
Total Level 1, Level 2, and Level 3 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	17,972		15,851
Total Level 1, Level 2, and Level 3 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	$ 5,194		$ 3,880

[1] Excluded from the table above are partially-owned investments, investment funds, and limited partnerships of $13,288 million, policy loans of $389 million, and other investments of $47 million at June 30, 2023, measured using NAV as a practical expedient.

[2] Excluded from the table above are partially-owned investments, investment funds, and limited partnerships of $12,355 million, policy loans of $343 million and other investments of $47 million at December 31, 2022, measured using NAV as a practical expedient.

[3] Refer to Note 11 for additional information on Market risk benefits.

[4] Refer to Note 11 for additional information on Market risk benefits.