Contingencies - Additional Information (Detail) (USD $)				12 Months Ended
	Dec. 31, 2012 Lower Limit	Dec. 31, 2012 Upper Limit	Aug. 19, 2011 United Guaranty [Member]	Dec. 31, 2012 Consent Order Foreclosure Actions [Member]	Dec. 31, 2012 Consent Order Foreclosure Prevention Actions [Member]	Dec. 31, 2012 Consent Order Potential Claims per Instance [Member] Lower Limit	Dec. 31, 2012 Consent Order Potential Claims per Instance [Member] Upper Limit	Dec. 31, 2012 Potential Statutory Civil Penalty per Violation [Member] Lower Limit	Dec. 31, 2012 Potential Statutory Civil Penalty per Violation [Member] Upper Limit
Aggregate range of reasonably possible losses on legal matters in excess of the accrued liability	$ 0	$ 300,000,000
Contingent Receipt, Judgement Award for Damages			34,000,000
Contingent Receipt, Judgement Interest Award			6,000,000
Contingent Receipt, Judgement Award for Claims Fees			5,000,000
Contingent Receipt, Total Judgment Award			45,000,000
Loss Contingency, Damages Sought, Value				$ 63,000,000	$ 100,000,000	$ 500	$ 125,000	$ 5,500	$ 11,000