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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Casualty	$ (5)	$ (6)	$ (5)	$ (6)
Property	(4)	13	11	12
Energy and Marine	9	(5)	8	(5)
Specialty	(1)	(4)	(1)	(3)
Total pretax (favorable) unfavorable development	$ (1)	$ (2)	$ 13	$ (2)