Investments and Cash - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	$ 10,545	$ 11,023
Other invested assets	170	169
Internally managed portfolio	10,715	11,192
Fixed Maturities, Managed Internally [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	1,208	1,266
Other Invested Assets, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	113	114
Other, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	58	55
Internally Managed Portfolio [Member]
Schedule of Cost-method Investments [Line Items]
Internally managed portfolio	$ 1,379	$ 1,435