Investments and Cash - Internally Managed Investment Portfolio (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	$ 11,258	$ 10,615
Other invested assets	126	170
Internally managed portfolio	11,384	10,785
Fixed Maturities, Managed Internally [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	835	761
Other Invested Assets, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	46	82
Other, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	79	88
Internally Managed Portfolio [Member]
Schedule of Cost-method Investments [Line Items]
Internally managed portfolio	$ 960	$ 931