Fair value measurements (Financial Instruments Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2024		Dec. 31, 2023		Jun. 30, 2023
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	$ 107,840		$ 106,571
Equity securities	3,792		3,455
Short-term investments	4,546		4,551
Other Investments	7,513		5,527
Securities lending collateral	1,889		1,299
Separate account assets	5,834		5,573		$ 5,574
Market risk benefits	576		771
Private equities	14,365		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	14,365		14,078
Policy Loans
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other Investments	1,029		702
U.S. Treasury / Agency
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,741		3,590
Non-U.S.
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	34,918		35,164
Corporate and asset-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	43,620		42,830
Mortgage-backed securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	24,614		22,058
Municipal
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	1,947		2,929
Level 1 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	2,128		2,911
Equity securities	3,692		3,368
Short-term investments	2,822		1,915
Other Investments	581	[1]	589	[2]
Securities lending collateral	0		0
Investment derivatives	41		54
Derivatives designated as hedging instruments	0		0
Other derivative instruments	1
Separate account assets	5,749		5,482
Total assets measured at fair value	15,014	[1],[3]	14,319	[2],[4]
Investment derivatives	169		136
Derivatives designated as hedging instruments	0		0
Other derivative instruments, liability	2		37
Market risk benefits	0	[5]	0	[6]
Total liabilities measured at fair value	171		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	2,128		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	102,351		100,339
Equity securities	0		0
Short-term investments	1,712		2,633
Other Investments	5,903	[1]	4,236	[2]
Securities lending collateral	1,889		1,299
Investment derivatives	0		0
Derivatives designated as hedging instruments	127		136
Other derivative instruments	0
Separate account assets	85		91
Total assets measured at fair value	112,067	[1],[3]	108,734	[2],[4]
Investment derivatives	0		0
Derivatives designated as hedging instruments	96		128
Other derivative instruments, liability	5		5
Market risk benefits	0	[5]	0	[6]
Total liabilities measured at fair value	101		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	613		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	34,286		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	40,911		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	24,594		22,051
Level 2 | Municipal | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	1,947		2,929
Level 3 | Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Debt Securities, Available-for-Sale	3,361		3,321
Equity securities	100		87
Short-term investments	12		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	3,473	[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	576	[5]	771	[6]
Total liabilities measured at fair value	576		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	632		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	2,709		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	20		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	107,840		106,571
Equity securities	3,792		3,455
Short-term investments	4,546		4,551
Other Investments	6,484	[1]	4,825	[2]
Securities lending collateral	1,889		1,299
Investment derivatives	41		54
Derivatives designated as hedging instruments	127		136
Other derivative instruments	1
Separate account assets	5,834		5,573
Total assets measured at fair value	130,554	[1],[3]	126,464	[2],[4]
Investment derivatives	169		136
Derivatives designated as hedging instruments	96		128
Other derivative instruments, liability	7		42
Market risk benefits	576	[5]	771	[6]
Total liabilities measured at fair value	848		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	2,741		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	34,918		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	43,620		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	24,614		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	$ 1,947		$ 2,929

[1] Excluded from the table above are other investments of $1,029 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 $14,365 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.