Claim and Claim Adjustment Expense Reserves (International - Detail of Development Recorded) (Details) - International - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 1	$ 0
Other Professional Liability	1	(1)
Liability	0	0
Property & Marine	(2)	1
Other	0	(2)
Total pretax (favorable) unfavorable development	$ 0	$ (2)