Concentrations of Credit Risk Estimated Benefit from Mortgage Insurers (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Risks and Uncertainties [Abstract]
Contractual mortgage insurance benefit	$ 7,117		$ 9,993
Less: Collectability adjustment	459	[1]	708	[1]
Estimated benefit included in total loss reserves	$ 6,658		$ 9,285

[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.