Litigation and Contingencies (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Loan	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Class action complaint under RESPA [Abstract]
Civil penalty	$ 2,650,000
Countrywide dispute [Abstract]
Number of rescindable loans affected by Company's decision to suspend rescissions for Countrywide	2,300
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for Countrywide	170,000,000
Number of rescindable loans affected by Company's decision to suspend rescissions for a specific customer	300
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for a specific customer	20,000,000
Other Legal Proceedings [Abstract]
Underwriting remedy expense		27,000,000	23,000,000	19,000,000
Class Action Complaint Under RESPA [Member] | Pending Litigation [Member]
Class action complaint under RESPA [Abstract]
Number of lawsuits	12
Number of cases dismissed	4
Number of similar cases filed naming various mortgage lenders and mortgage insurers as defendants	8
Countrywide Dispute [Member]
Countrywide dispute [Abstract]
Average paid claim reduction due to curtailments (in hundredths)	4.70%	4.10%
Number of days after claim paid within which objection must be received for review	90 days
Curtailment and other adjustments objected	40,000,000
Countrywide Dispute [Member] | Pending Litigation [Member]
Countrywide dispute [Abstract]
Amount of damages sought	700,000,000
Mitigation of paid losses	445,000,000
Number of rescindable loans affected by Company's decision to suspend rescissions for Countrywide	2,300
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for Countrywide	170,000,000
Number of rescindable loans affected by Company's decision to suspend rescissions for a specific customer	300
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for a specific customer	20,000,000
Increase in loss reserves for the probable settlement agreements	100,000,000
Mitigation of incurred losses since January 2008	2,900,000,000
Mitigation on paid losses, excluding deductible amounts	2,900,000,000
Amount excluded from mitigation losses that would have been applied to a deductible	600,000,000
Total loss reserves, estimated benefit from rescissions	$ 200,000,000
Lawsuits alleging improper recording and foreclosure activities by MERS [Member] | Pending Litigation [Member]
Lawsuits alleging improper recording and foreclosure activities by MERS [Abstract]
Number of lawsuits naming non-insurance subsidiary as defendant	8
Number of cases pending	2
Number of other lawsuits naming subsidiary as defendant that were dismissed	6