Statutory Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) jurisdiction	Mar. 31, 2019 USD ($)	Jun. 30, 2019 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, including reinsurance affiliates, at end of period			10.0 to 1
Risk-to-capital ratio for combined insurance operations	10.0		10.0
Purchases of tax and loss bonds	$ 74
Percentage of statutory policyholders surplus used to determine maximum allowable dividends (as a percent)	10.00%		10.00%
Mortgage Guaranty Insurance Corporation
Statutory capital requirements [Abstract]
Maximum risk-to-capital ratio			25
Risk to capital ratio at end of period			10.1 to 1
Risk-to-capital ratio	10.1		10.1
Amount of policyholders position above or below required MPP	$ 2,700		$ 2,700
Amount of required MPP	1,600		$ 1,600
Dividends paid to the parent company	$ 70	$ 70
Adjusted statutory net income measurement period (in years)			3 years
Adjusted statutory net income dividend payment measurement period (in years)			2 years