Investments and Cash - Internally Managed Investment Portfolio (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	$ 10,182	$ 11,258
Other invested assets	132	126
Internally managed portfolio	10,314	11,384
Fixed Maturities, Managed Internally [Member]
Schedule of Cost-method Investments [Line Items]
Fixed-maturity securities	721	835
Other Invested Assets, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	41	46
Other, Internally Managed [Member]
Schedule of Cost-method Investments [Line Items]
Other invested assets	91	79
Internally Managed Portfolio [Member]
Schedule of Cost-method Investments [Line Items]
Internally managed portfolio	$ 853	$ 960