Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2023		Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	$ 88,364		$ 85,220
Equity securities, at fair value	942		827
Other Short-Term Investments	3,693		4,960
Other investments, at fair value	14,192		13,696
Securities lending collateral	1,582		1,523
Separate account assets	5,300		5,190
Market risk benefits	830		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	12,805		12,355
Policy Loans
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other investments, at fair value	358		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	2,679		2,626
Non-U.S.
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	27,392		25,908
Corporate and asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	38,460		36,955
Mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	16,102		15,851
Municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,731		3,880
Level 1 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	2,119		2,100
Equity securities, at fair value	854		737
Other Short-Term Investments	1,856		3,108
Other investments, at fair value	559	[1]	552
Securities lending collateral	0		0
Investment derivative instruments	59		82
Derivatives designated as hedging instruments	0		0
Other derivative instruments	5		33
Separate account assets	5,198		5,101
Total assets measured at fair value	10,650	[1]	11,713
Investment derivatives	158		139
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	45
Market risk benefits	0	[2]	0
Total liabilities measured at fair value	203		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	2,119		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	83,130		80,096
Equity securities, at fair value	0		0
Other Short-Term Investments	1,830		1,849
Other investments, at fair value	423	[1]	399
Securities lending collateral	1,582		1,523
Investment derivative instruments	0		0
Derivatives designated as hedging instruments	8		17
Other derivative instruments	0		0
Separate account assets	102		89
Total assets measured at fair value	87,075	[1]	83,973
Investment derivatives	0		0
Derivatives designated as hedging instruments	82		53
Other derivative instruments, liability	2
Market risk benefits	0	[2]	0
Total liabilities measured at fair value	84		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	560		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	26,831		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	35,916		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	16,092		15,840
Level 2 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,731		3,880
Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale, Fair Value	3,115		3,024
Equity securities, at fair value	88		90
Other Short-Term Investments	7		3
Other investments, at fair value	0	[1]	0
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	3,210	[1]	3,117
Investment derivatives	0		0
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	0
Market risk benefits	830	[2]	800
Total liabilities measured at fair value	830		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	561		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	2,544		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	88,364		85,220
Equity securities, at fair value	942		827
Other Short-Term Investments	3,693		4,960
Other investments, at fair value	982	[1]	951
Securities lending collateral	1,582		1,523
Investment derivative instruments	59		82
Derivatives designated as hedging instruments	8		17
Other derivative instruments	5		33
Separate account assets	5,300		5,190
Total assets measured at fair value	100,935	[1]	98,803
Investment derivatives	158		139
Derivatives designated as hedging instruments	82		53
Other derivative instruments, liability	47
Market risk benefits	830	[2]	800
Total liabilities measured at fair value	1,117		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	2,679		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	27,392		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	38,460		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	16,102		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	$ 3,731		$ 3,880

[1] Excluded from the table above are partially-owned investments, investment funds, and limited partnerships of $12,805 million, policy loans of $358 million, and other investments of $47 million at March 31, 2023, measured using NAV as a practical expedient.

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