Financial Guaranty Insurance Contracts (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Minimum
Financial Guaranty Insurance Premiums
Period after end of reporting period within which some of the company's ceding companies report premium data (in days)	30 days
Estimated after-tax cumulative effect on opening retained earnings due to adoption of Accounting Standards Update No. 2010-26	$ (60)
Pre-tax cumulative effect on DAC due to adoption of Accounting Standards Update No. 2010-26	90
Maximum
Financial Guaranty Insurance Premiums
Period after end of reporting period within which some of the company's ceding companies report premium data (in days)	90 days
Estimated after-tax cumulative effect on opening retained earnings due to adoption of Accounting Standards Update No. 2010-26	(80)
Pre-tax cumulative effect on DAC due to adoption of Accounting Standards Update No. 2010-26	$ 110