Claim and Claim Adjustment Expense and Future Policy Benefit 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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Casualty	$ (6)	$ (5)	$ (11)	$ (11)
Property	3	2	14	14
Energy and Marine	1	(5)	9	(10)
Specialty	3	6	2	3
Total pretax (favorable) unfavorable development	$ 1	$ (2)	$ 14	$ (4)