Statutory Information (Details) $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended
	Aug. 31, 2021 USD ($)	Dec. 31, 2021	Jun. 30, 2021 USD ($) jurisdiction	Sep. 30, 2021
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			8.9 to 1
Risk-to-capital ratio for combined insurance operations			8.9
Forecast
Statutory capital requirements [Abstract]
Regulatory restrictions on payment of dividends, percentage of available assets exceeding minimum required assets		0.15		0.50
Mortgage Guaranty Insurance Corporation
Statutory capital requirements [Abstract]
Maximum risk-to-capital ratio			25
Risk to capital ratio at end of period			8.9 to 1
Risk-to-capital ratio			8.9
Amount of policyholders position above or below required MPP			$ 3,500
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
Mortgage Guaranty Insurance Corporation | Subsequent Event
Statutory capital requirements [Abstract]
Dividends paid to the parent company	$ 150