Statutory Capital (Details) (USD $)	9 Months Ended
	Sep. 30, 2014 Jurisdiction	Dec. 31, 2013
Related Party Transaction [Line Items]
Number of jurisdictions with risk-to-capital requirements	16
Statutory capital requirements [Abstract]
Maximum permitted risk-to-capital ratio commonly applied	25 to 1
Risk-to-capital ratio on a combined basis at end of period	17.0 to 1
Percentage of surplus as regards policyholders (in hundredths)	10.00%
Statutory deferred tax assets admitted	$ 134,000,000	$ 138,000,000
Mortgage Guaranty Insurance Corporation [Member]
Statutory capital requirements [Abstract]
Risk to capital ratio at end of period	15.0 to 1
Amount of policyholders position above or below required MPP	605,000,000
Amount of required MPP	1,000,000,000
MGIC Indemnity Corporation [Member]
Statutory capital requirements [Abstract]
Statutory capital of subsidiary	466,000,000
Risk in force, net of reinsurance, of subsidiary	$ 547,000,000