Statutory Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2021	Sep. 30, 2021 USD ($) jurisdiction	Sep. 30, 2021 USD ($) jurisdiction
Statutory capital requirements [Abstract]
Number of jurisdictions with risk-to-capital requirements (in jurisdictions) | jurisdiction		16	16
Maximum permitted risk-to-capital ratio commonly applied			25 to 1
Risk to capital ratio of combined insurance operations at end of period			9.0 to 1
Risk-to-capital ratio for combined insurance operations		9.0	9.0
Forecast
Statutory capital requirements [Abstract]
Regulatory restrictions on payment of dividends, percentage of available assets exceeding minimum required assets	0.15
Mortgage Guaranty Insurance Corporation
Statutory capital requirements [Abstract]
Maximum risk-to-capital ratio			25
Risk to capital ratio at end of period			9.0 to 1
Risk-to-capital ratio		9.0	9.0
Amount of policyholders position above or below required MPP		$ 3,600	$ 3,600
Amount of required MPP		1,800	$ 1,800
Dividends paid to the parent company		$ 150
Percentage of statutory policyholders surplus used to determine maximum allowable dividends (as a percent)		10.00%	10.00%
Adjusted statutory net income measurement period (in years)			3 years
Adjusted statutory net income dividend payment measurement period (in years)			2 years