Claim and Claim Adjustment Expense Reserves (International - Net prior year claim and allocated claim adjustment expense reserve development) (Details) - International - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Casualty	$ (4)	$ (5)	$ (3)	$ (11)
Property, Energy and Marine	(14)	9	(17)	10
Specialty	21	(4)	22	(2)
Total pretax (favorable) unfavorable development	$ 3	$ 0	$ 2	$ (3)