Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2023		Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	$ 99,766		$ 85,220
Equity securities, at fair value	3,395		827
Other Short-Term Investments	5,454		4,960
Other investments	5,583		1,341
Securities lending collateral	1,469		1,523
Separate account assets	5,306		5,190
Market risk benefits	770		800
Alternative Investment	13,362		12,355
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Alternative Investment	13,362		12,355
Policy Loans
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other investments	603		343
Other Investments
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other investments	47		47
U.S. Treasury / Agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	3,681		2,626
Non-U.S.
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	32,717		25,908
Corporate and asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	40,855		36,955
Mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	19,605		15,851
Municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,908		3,880
Level 1 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	3,084		2,100
Equity securities, at fair value	3,310		737
Other Short-Term Investments	2,546		3,108
Other investments	569	[1]	552	[2]
Securities lending collateral	0		0
Investment derivative instruments	42		82
Derivatives designated as hedging instruments	0		0
Other derivative instruments	53		33
Separate account assets	5,217		5,101
Total assets measured at fair value	14,821	[1]	11,713	[2]
Investment derivatives	168		139
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	0
Market risk benefits	0	[3]	0	[4]
Total liabilities measured at fair value	168		139
Level 1 | U.S. Treasury / Agency | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	3,084		2,100
Level 1 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	0		0
Level 1 | Corporate and asset-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	0		0
Level 1 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	0		0
Level 1 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	0		0
Level 2 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	93,455		80,096
Equity securities, at fair value	0		0
Other Short-Term Investments	2,906		1,849
Other investments	4,364	[1]	399	[2]
Securities lending collateral	1,469		1,523
Investment derivative instruments	0		0
Derivatives designated as hedging instruments	48		17
Other derivative instruments	0		0
Separate account assets	89		89
Total assets measured at fair value	102,331	[1]	83,973	[2]
Investment derivatives	0		0
Derivatives designated as hedging instruments	68		53
Other derivative instruments, liability	4
Market risk benefits	0	[3]	0	[4]
Total liabilities measured at fair value	72		53
Level 2 | U.S. Treasury / Agency | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	597		526
Level 2 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	32,084		25,344
Level 2 | Corporate and asset-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	38,286		34,506
Level 2 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	19,580		15,840
Level 2 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,908		3,880
Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	3,227		3,024
Equity securities, at fair value	85		90
Other Short-Term Investments	2		3
Other investments	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	3,314	[1]	3,117	[2]
Investment derivatives	0		0
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	0
Market risk benefits	770	[3]	800	[4]
Total liabilities measured at fair value	770		800
Level 3 | U.S. Treasury / Agency | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	0		0
Level 3 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	633		564
Level 3 | Corporate and asset-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,569		2,449
Level 3 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	25		11
Level 3 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	0		0
Total Level 1, Level 2, and Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	99,766		85,220
Equity securities, at fair value	3,395		827
Other Short-Term Investments	5,454		4,960
Other investments	4,933	[1]	951	[2]
Securities lending collateral	1,469		1,523
Investment derivative instruments	42		82
Derivatives designated as hedging instruments	48		17
Other derivative instruments	53		33
Separate account assets	5,306		5,190
Total assets measured at fair value	120,466	[1]	98,803	[2]
Investment derivatives	168		139
Derivatives designated as hedging instruments	68		53
Other derivative instruments, liability	4
Market risk benefits	770	[3]	800	[4]
Total liabilities measured at fair value	1,010		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]
Debt Securities, Available-for-Sale	3,681		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]
Debt Securities, Available-for-Sale	32,717		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]
Debt Securities, Available-for-Sale	40,855		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]
Debt Securities, Available-for-Sale	19,605		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]
Debt Securities, Available-for-Sale	$ 2,908		$ 3,880

[1] Excluded from the table above are policy loans of $603 million, and other investments of $47 million at September 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 $13,362 million at September 30, 2023, measured using NAV as a practical expedient.

[2] Excluded from the table above are policy loans of $343 million and other investments of $47 million at December 31, 2022, 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 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.