Investments and Cash - Internally Managed Investment Portfolio (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	$ 10,823	$ 11,023
Other invested assets	162	169
Total investment portfolio	10,985	11,192
Fixed Maturities, Managed Internally [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	1,492	1,266
Other Invested Assets, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	107	114
Other, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	55	55
Internally Managed Portfolio [Member]
Schedule of Cost-method Investments [Line Items]
Total investment portfolio	$ 1,654	$ 1,435