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
	Mar. 31, 2019	Mar. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Casualty	$ 0	$ 0
Property	15	(1)
Energy and Marine	(1)	0
Specialty	0	1
Total pretax (favorable) unfavorable development	$ 14	$ 0