Unpaid losses and loss expenses Unpaid losses and loss expenses (PPD table) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	$ (200)	$ (247)	$ (396)	$ (487)
North America Commercial P&C Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(146)	(287)	(218)	(395)
North America Commercial P&C Insurance [Member] | Auto Liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	119	123	125	116
North America Commercial P&C Insurance [Member] | General Liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		(132)		(136)
North America Commercial P&C Insurance [Member] | Accident and Health Insurance Product Line [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development				(78)
North America Personal P&C Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(33)	(3)	(16)	(54)
North American Agriculture Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(3)	0	(3)	(26)
Overseas General Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(61)	(173)	(204)	(233)
Overseas General Insurance [Member] | Property, Liability and Casualty Insurance Product Line
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	61
Overseas General Insurance [Member] | Property, Liability and Casualty Insurance Product Line | Catastrophe [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development			110
Global Reinsurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(17)	25	(25)	22
Corporate Segment [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development			70	199
Corporate Segment [Member] | Other [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	60		70
Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(128)	(165)	(343)	(393)
Short Tail [Member] | North America Commercial P&C Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(7)	(21)	(88)	(109)
Short Tail [Member] | North America Personal P&C Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(33)	(3)	(16)	(54)
Short Tail [Member] | North American Agriculture Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(3)	0	(3)	(26)
Short Tail [Member] | Overseas General Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(61)	(173)	(204)	(233)
Short Tail [Member] | Overseas General Insurance [Member] | Accident and Health Insurance Product Line [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		173		233
Short Tail [Member] | Global Reinsurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(24)	32	(32)	29
Short Tail [Member] | Corporate Segment [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(72)	(82)	(53)	(94)
Long Tail [Member] | North America Commercial P&C Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(139)	(266)	(130)	(286)
Long Tail [Member] | North America Personal P&C Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
Long Tail [Member] | North American Agriculture Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
Long Tail [Member] | Overseas General Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
Long Tail [Member] | Global Reinsurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	7	(7)	7	(7)
Long Tail [Member] | Corporate Segment [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	$ 60	$ 191	$ 70	199
Long Tail [Member] | Corporate Segment [Member] | Other [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development				$ 155