Unpaid losses and loss expenses Unpaid losses and loss expenses (Details) (Supplementary PPD) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
North America Commercial P&C Insurance - Workers' Compensation [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	$ (223)
North America Commercial P&C Insurance - Workers' Compensation [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(98)
North America Commercial P&C Insurance - Workers' Compensation [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	(125)
North America Commercial P&C Insurance - Liability [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(207)
North America Commercial P&C Insurance - Liability [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(86)
North America Commercial P&C Insurance - Liability [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	(121)
North America Commercial P&C Insurance - Other Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	21
North America Commercial P&C Insurance - Other Casualty [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(7)
North America Commercial P&C Insurance - Other Casualty [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	28
North America Commercial P&C Insurance - Non-Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(280)
North America Commercial P&C Insurance - Non-Casualty [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(3)
North America Commercial P&C Insurance - Non-Casualty [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	(277)
North America Personal P&C Insurance [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(295)
North America Personal P&C Insurance [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(2)
North America Personal P&C Insurance [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	(293)
Overseas General Insurance - Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(98)
Overseas General Insurance - Casualty [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(76)
Overseas General Insurance - Casualty [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	(22)
Overseas General Insurance - Non-Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(216)
Overseas General Insurance - Non-Casualty [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(6)
Overseas General Insurance - Non-Casualty [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	(210)
Global Reinsurance - Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(29)
Global Reinsurance - Casualty [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(27)
Global Reinsurance - Casualty [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	(2)
Global Reinsurance - Non-Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	30
Global Reinsurance - Non-Casualty [Member] | prior to 2012
Supplementary PPD [Line Items]
Short-Duration PPD	(4)
Global Reinsurance - Non-Casualty [Member] | 2012 - 2021
Supplementary PPD [Line Items]
Short-Duration PPD	$ 34