Investments and Cash (Details 4) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Amortized Cost
Due within one year	$ 269
Due after one year through five years	1,602
Due after five years through 10 years	2,451
Due after 10 years	3,601
Estimated Fair Value
Due within one year	273
Due after one year through five years	1,674
Due after five years through 10 years	2,554
Due after 10 years	3,729
Estimated fair value	9,873		10,056
Fixed maturity securities held under trust for the benefit of reinsured companies	360		368
Eligible securities deposited for the benefit of policyholders	22		27
Percentage of the value of letter of credit of fixed maturity investments held in segregated account as collateral for letter of credit	120.00%
Fixed maturity investments in a segregated portfolio primarily to provide collateral for a LOC	3.5		3.5
Fair market value of company's pledged securities	681		660
RMBS
Amortized Cost
Amortized cost	1,157
Estimated Fair Value
Estimated fair value	1,120
CMBS
Amortized Cost
Amortized cost	507
Estimated Fair Value
Estimated fair value	523
Fixed maturity securities
Amortized Cost
Amortized cost	9,587	[1]	9,346	[1]
Estimated Fair Value
Estimated fair value	$ 9,873

[1] Ratings in the tables above represent the lower of the Moody’s and S&P classifications except for bonds purchased for loss mitigation or risk management strategies, which use internal ratings classifications. The Company’s portfolio consists primarily of high-quality, liquid instruments.