Unpaid losses and loss expenses Unpaid losses and loss expenses (Supplementary PPD) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)
North America Commercial P&C Insurance - Workers' Compensation [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	$ (437)
North America Commercial P&C Insurance - Workers' Compensation [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	(132)
North America Commercial P&C Insurance - Workers' Compensation [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	(305)
North America Commercial P&C Insurance - Liability [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	243
North America Commercial P&C Insurance - Liability [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	98
North America Commercial P&C Insurance - Liability [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	145
North America Commercial P&C Insurance - Other Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	133
North America Commercial P&C Insurance - Other Casualty [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	56
North America Commercial P&C Insurance - Other Casualty [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	77
North America Commercial P&C Insurance - Non-Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(330)
North America Commercial P&C Insurance - Non-Casualty [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	(11)
North America Commercial P&C Insurance - Non-Casualty [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	(319)
North America Personal P&C Insurance [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(128)
North America Personal P&C Insurance [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	(5)
North America Personal P&C Insurance [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	(123)
Overseas General Insurance - Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(68)
Overseas General Insurance - Casualty [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	8
Overseas General Insurance - Casualty [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	(76)
Overseas General Insurance - Non-Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(280)
Overseas General Insurance - Non-Casualty [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	(10)
Overseas General Insurance - Non-Casualty [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	(270)
Global Reinsurance - Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	(8)
Global Reinsurance - Casualty [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	(7)
Global Reinsurance - Casualty [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	(1)
Global Reinsurance - Non-Casualty [Member]
Supplementary PPD [Line Items]
Short-Duration PPD	30
Global Reinsurance - Non-Casualty [Member] | Accident years prior to 2013
Supplementary PPD [Line Items]
Short-Duration PPD	(4)
Global Reinsurance - Non-Casualty [Member] | Accident years 2013 - 2022
Supplementary PPD [Line Items]
Short-Duration PPD	$ 34