Investments - Fixed Maturities by Maturity Periods (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Amortized Cost:
Due in one year or less	$ 1,075
Due after one year through five years	4,942
Due after five years through ten years	4,707
Due after ten years	2,645
Mortgage and other asset-backed securities	930
Total amortized cost	14,299
Fair Value:
Due in one year or less	1,094
Due after one year through five years	5,312
Due after five years through ten years	5,073
Due after ten years	3,247
Mortgage and other asset-backed securities	1,025
Total fair value	$ 15,751	$ 17,689