Investments - Fixed Maturities by Maturity Periods (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Amortized Cost:
Due in one year or less	$ 1,057
Due after one year through five years	5,023
Due after five years through ten years	4,665
Due after ten years	2,596
Mortgage and other asset-backed securities	948
Total amortized cost	14,289
Fair Value:
Due in one year or less	1,077
Due after one year through five years	5,407
Due after five years through ten years	4,982
Due after ten years	3,133
Mortgage and other asset-backed securities	1,040
Total fair value	$ 15,639	$ 17,689