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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Casualty	$ (6)	$ (5)	$ (6)	$ (5)
Property, Energy and Marine	1	5	1	19
Specialty	2	(1)	2	(1)
Total pretax (favorable) unfavorable development	$ (3)	$ (1)	$ (3)	$ 13