Investments and Cash - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	$ 11,495	$ 10,823
Other invested assets	96	162
Total investment portfolio	11,591	10,985
Fixed Maturities, Managed Internally [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	1,220	1,492
Other Invested Assets, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	20	107
Other, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	76	55
Internally Managed Portfolio [Member]
Schedule of Cost-method Investments [Line Items]
Total investment portfolio	$ 1,316	$ 1,654