Unpaid losses and loss expenses Unpaid losses and loss expenses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	$ (200)	$ (247)	$ (396)	$ (487)
Unpaid losses and loss expenses	76,480	73,448	76,480	73,448	$ 75,747	$ 72,330
Net loss and loss expenses paid, Prior Years			7,527	6,566
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease), Gross			733
Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(72)	(82)	(53)	(94)
Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(128)	(165)	(343)	(393)
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] | Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(139)	(266)	(130)	(286)
North America Commercial P&C Insurance [Member] | Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(7)	(21)	(88)	(109)
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 Commercial P&C Insurance [Member] | Workers' Compensation Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(264)	(286)	(308)	(328)
North America Agricultural Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(3)	0	(3)	(26)
North America Agricultural Insurance [Member] | Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
North America Agricultural Insurance [Member] | Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(3)	0	(3)	(26)
Corporate Segment [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development			70	199
Corporate Segment [Member] | Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	60	191	70	199
Corporate Segment [Member] | Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
Corporate Segment [Member] | Other [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	60		70
Corporate Segment [Member] | Other [Member] | Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development				155
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] | Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
Overseas General Insurance [Member] | Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(61)	(173)	(204)	(233)
Overseas General Insurance [Member] | Accident and Health Insurance Product Line [Member] | Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		173		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
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 America Personal P&C Insurance [Member] | Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	0	0	0	0
North America Personal P&C Insurance [Member] | Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(33)	(3)	(16)	(54)
Global Reinsurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	(17)	25	(25)	22
Global Reinsurance [Member] | Long Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	7	(7)	7	(7)
Global Reinsurance [Member] | Short Tail [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development	$ (24)	$ 32	$ (32)	$ 29