Unpaid losses and loss expenses Unpaid losses and loss expenses (PPD table) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (876)	$ (926)	$ (395)
Prior Period Development Percentage Opening Net Unpaid Reserves	[1]	1.50%	1.70%	0.80%
Long Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ 58	$ (44)	$ (313)
Short Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		(934)	(882)	(82)
North America Commercial P&C Insurance [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (562)	$ (762)	$ (702)
Prior Period Development Percentage Opening Net Unpaid Reserves	[1]	1.00%	1.40%	1.40%
North America Commercial P&C Insurance [Member] | Long Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (229)	$ (482)	$ (672)
North America Commercial P&C Insurance [Member] | Short Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		(333)	(280)	(30)
North America Personal P&C Insurance [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (186)	$ (305)	$ 63
Prior Period Development Percentage Opening Net Unpaid Reserves	[1]	0.30%	0.60%	0.10%
North America Personal P&C Insurance [Member] | Long Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ 0	$ 0	$ 0
North America Personal P&C Insurance [Member] | Short Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		(186)	(305)	63
North America Agricultural Insurance [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (61)	$ 10	$ (10)
Prior Period Development Percentage Opening Net Unpaid Reserves	[1]	0.10%	0.00%	0.00%
North America Agricultural Insurance [Member] | Long Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ 0	$ 0	$ 0
North America Agricultural Insurance [Member] | Short Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		(61)	10	(10)
Overseas General Insurance [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (448)	$ (441)	$ (150)
Prior Period Development Percentage Opening Net Unpaid Reserves	[1]	0.80%	0.80%	0.30%
Overseas General Insurance [Member] | Long Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (65)	$ (106)	$ (49)
Overseas General Insurance [Member] | Short Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		(383)	(335)	(101)
Global Reinsurance [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ 22	$ 3	$ (29)
Prior Period Development Percentage Opening Net Unpaid Reserves	[1]	0.00%	0.00%	0.10%
Global Reinsurance [Member] | Long Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ (7)	$ (25)	$ (25)
Global Reinsurance [Member] | Short Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		29	28	(4)
Corporate Segment [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ 359	$ 569	$ 433
Prior Period Development Percentage Opening Net Unpaid Reserves	[1]	0.60%	1.10%	0.90%
Corporate Segment [Member] | Long Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ 359	$ 569	$ 433
Corporate Segment [Member] | Short Tail [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Net Prior Period Development		$ 0	$ 0	$ 0

[1] Calculated based on the beginning of period consolidated net unpaid losses and loss expenses.