Statutory Information (Details) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019 USD ($) jurisdiction	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) 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				9.8 to 1
Risk-to-capital ratio for combined insurance operations	9.8			9.8
Purchases of tax and loss bonds				$ 126
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				9.9 to 1
Risk-to-capital ratio	9.9			9.9
Amount of policyholders position above or below required MPP	$ 2,900			$ 2,900
Amount of required MPP	1,600			$ 1,600
Dividends paid to the parent company	$ 70	$ 70	$ 70
Adjusted statutory net income measurement period (in years)				3 years
Adjusted statutory net income dividend payment measurement period (in years)				2 years