Concentrations of Credit Risk Estimated Benefit from Mortgage Insurers (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Risks and Uncertainties [Abstract]
Contractual mortgage insurance benefit	$ 9,993		$ 15,099
Less: Collectability adjustment	708	[1]	2,867	[1]
Estimated benefit included in total loss reserves	$ 9,285		$ 12,232

[1] Represents an adjustment that reduces the contractual benefit for our assessment of our mortgage insurer counterparties’ inability to fully pay the contractual mortgage insurance claims.