Statutory Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) jurisdiction
Statutory capital requirements [Abstract]
Number of jurisdictions with risk-to-capital requirements (in jurisdictions) | jurisdiction	16
Maximum permitted risk-to-capital ratio commonly applied	25 to 1
Risk to capital ratio of combined insurance operations at end of period	8.8 to 1
Risk-to-capital ratio for combined insurance operations	8.8
Mortgage Guaranty Insurance Corporation
Statutory capital requirements [Abstract]
Maximum risk-to-capital ratio	25
Risk to capital ratio at end of period	8.8 to 1
Risk-to-capital ratio	8.8
Amount of policyholders position above or below required MPP	$ 3,400
Amount of required MPP	1,700
Dividends paid to the parent company	$ 0
Percentage of statutory policyholders surplus used to determine maximum allowable dividends (as a percent)	10.00%
Adjusted statutory net income measurement period (in years)	3 years
Adjusted statutory net income dividend payment measurement period (in years)	2 years