Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2024		Dec. 31, 2023		Sep. 30, 2023
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	$ 117,265		$ 106,571
Equity securities	4,404		3,455
Short-term investments	4,375		4,551
Other investments	8,155		5,527
Securities lending collateral	1,927		1,299
Separate account assets	5,996		5,573		$ 5,306
Market risk benefits	748		771
Private equities	14,405		14,078
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Private equities	14,405		14,078
Policy Loans
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other investments	1,115		702
U.S. Treasury / Agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,629		3,590
Non-U.S.
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	37,501		35,164
Corporate and asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	46,693		42,830
Mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	28,474		22,058
Municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	1,968		2,929
Level 1 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	1,979		2,911
Equity securities	4,286		3,368
Short-term investments	2,491		1,915
Other investments	616	[1]	589	[2]
Securities lending collateral	0		0
Investment derivatives	42		54
Derivatives designated as hedging instruments	0		0
Separate account assets	5,919		5,482
Total assets measured at fair value	15,333	[1],[3]	14,319	[2],[4]
Investment derivatives	127		136
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	25		37
Market risk benefits	0	[5]	0	[6]
Total liabilities measured at fair value	152		173
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	1,979		2,911
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	111,823		100,339
Equity securities	0		0
Short-term investments	1,869		2,633
Other investments	6,424	[1]	4,236	[2]
Securities lending collateral	1,927		1,299
Investment derivatives	0		0
Derivatives designated as hedging instruments	150		136
Separate account assets	77		91
Total assets measured at fair value	122,270	[1],[3]	108,734	[2],[4]
Investment derivatives	0		0
Derivatives designated as hedging instruments	174		128
Other derivative instruments, liability	5		5
Market risk benefits	0	[5]	0	[6]
Total liabilities measured at fair value	179		133
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	650		679
Level 2 | Non-U.S. | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	36,862		34,472
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	43,915		40,208
Level 2 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	28,428		22,051
Level 2 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	1,968		2,929
Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	3,463		3,321
Equity securities	118		87
Short-term investments	15		3
Other investments	0	[1]	0	[2]
Securities lending collateral	0		0
Investment derivatives	0		0
Derivatives designated as hedging instruments	0		0
Separate account assets	0		0
Total assets measured at fair value	3,596	[1],[3]	3,411	[2],[4]
Investment derivatives	0		0
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	0		0
Market risk benefits	748	[5]	771	[6]
Total liabilities measured at fair value	748		771
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	639		692
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	2,778		2,622
Level 3 | Mortgage-backed securities | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	46		7
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	117,265		106,571
Equity securities	4,404		3,455
Short-term investments	4,375		4,551
Other investments	7,040	[1]	4,825	[2]
Securities lending collateral	1,927		1,299
Investment derivatives	42		54
Derivatives designated as hedging instruments	150		136
Separate account assets	5,996		5,573
Total assets measured at fair value	141,199	[1],[3]	126,464	[2],[4]
Investment derivatives	127		136
Derivatives designated as hedging instruments	174		128
Other derivative instruments, liability	30		42
Market risk benefits	748	[5]	771	[6]
Total liabilities measured at fair value	1,079		1,077
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	2,629		3,590
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	37,501		35,164
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	46,693		42,830
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	28,474		22,058
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	$ 1,968		$ 2,929

[1] Excluded from the table above are other investments of $1,115 million, principally policy loans, measured using NAV as a practical expedient.

[2] Excluded from the table above are other investments of $702 million, principally policy loans, measured using NAV as a practical expedient.

[3] Excluded from the table above are private equities of $14,405 million, measured using NAV as a practical expedient.

[4] Excluded from the table above are private equities of $14,078 million, measured using NAV as a practical expedient.

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

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