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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Casualty	$ (5)	$ (6)	$ (11)	$ (11)
Property, Energy and Marine	9	4	10	23
Specialty	(4)	3	(2)	2
Total pretax (favorable) unfavorable development	$ 0	$ 1	$ (3)	$ 14