Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2024		Dec. 31, 2023		Mar. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	$ 108,289		$ 106,571
Equity securities	3,769		3,455
Short-term investments	5,107		4,551
Other Investments	6,216		5,527
Securities lending collateral	1,708		1,299
Separate account assets	5,864		5,573		$ 5,300
Market risk benefits	611		771
Private equities	14,281		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	14,281		14,078
Policy Loans
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other Investments	736		702
U.S. Treasury / Agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,899		3,590
Non-U.S.
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	36,145		35,164
Corporate and asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	43,447		42,830
Mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	23,755		22,058
Municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,043		2,929
Level 1 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,251		2,911
Equity securities	3,668		3,368
Short-term investments	3,292		1,915
Other Investments	583	[1]	589	[2]
Securities lending collateral	0		0
Investment derivatives	28		54
Derivatives designated as hedging instruments	0		0
Other derivative instruments	1
Separate account assets	5,775		5,482
Total assets measured at fair value	15,598	[1],[3]	14,319	[2],[4]
Investment derivatives	144		136
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	22		37
Market risk benefits	0	[5]	0	[6]
Total liabilities measured at fair value	166		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	2,251		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	102,655		100,339
Equity securities	0		0
Short-term investments	1,810		2,633
Other Investments	4,897	[1]	4,236	[2]
Securities lending collateral	1,708		1,299
Investment derivatives	0		0
Derivatives designated as hedging instruments	149		136
Other derivative instruments	0
Separate account assets	89		91
Total assets measured at fair value	111,308	[1],[3]	108,734	[2],[4]
Investment derivatives	0		0
Derivatives designated as hedging instruments	110		128
Other derivative instruments, liability	6		5
Market risk benefits	0	[5]	0	[6]
Total liabilities measured at fair value	116		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	648		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	35,427		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	40,789		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	23,748		22,051
Level 2 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,043		2,929
Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	3,383		3,321
Equity securities	101		87
Short-term investments	5		3
Other Investments	0	[1]	0	[2]
Securities lending collateral	0		0
Investment derivatives	0		0
Derivatives designated as hedging instruments	0		0
Other derivative instruments	0
Separate account assets	0		0
Total assets measured at fair value	3,489	[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	611	[5]	771	[6]
Total liabilities measured at fair value	611		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	718		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	2,658		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	7		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	108,289		106,571
Equity securities	3,769		3,455
Short-term investments	5,107		4,551
Other Investments	5,480	[1]	4,825	[2]
Securities lending collateral	1,708		1,299
Investment derivatives	28		54
Derivatives designated as hedging instruments	149		136
Other derivative instruments	1
Separate account assets	5,864		5,573
Total assets measured at fair value	130,395	[1],[3]	126,464	[2],[4]
Investment derivatives	144		136
Derivatives designated as hedging instruments	110		128
Other derivative instruments, liability	28		42
Market risk benefits	611	[5]	771	[6]
Total liabilities measured at fair value	893		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	2,899		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	36,145		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	43,447		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	23,755		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	$ 2,043		$ 2,929

[1] Excluded from the table above are other investments of $736 million, principally policy loans at March 31, 2024, measured using NAV as a practical expedient.

[2] Excluded from the table above are other investments of $702 million, principally policy loans at December 31, 2023, measured using NAV as a practical expedient.

[3] Excluded from the table above are Private equities of $14,281 million at March 31, 2024, measured using NAV as a practical expedient.

[4] Excluded from the table above are Private equities of $14,078 million at December 31, 2023, measured using NAV as a practical expedient.

[5] Refer to Note 10 for additional information on Market risk benefits.

[6] Refer to Note 10 for additional information on Market risk benefits.