Capital Requirements (Details) $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($) jurisdiction	Mar. 31, 2016 USD ($)	Jun. 30, 2016 USD ($) jurisdiction	Dec. 31, 2015 USD ($)
Statutory capital requirements [Abstract]
Number of jurisdictions with risk-to-capital requirements | 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			13.2 to 1
Risk-to-capital ratio for combined insurance operations	13.2		13.2
Percentage of statutory policyholders surplus used to determine maximum allowable dividends	10.00%		10.00%
Mortgage Guaranty Insurance Corporation
Statutory capital requirements [Abstract]
Risk-to-capital ratio	11.6		11.6
Risk to capital ratio at end of period			11.6 to 1
Amount of policyholders position above or below required MPP	$ 1,300		$ 1,300
Amount of required MPP	1,100		$ 1,100
Cash dividends paid	$ 16	$ 16
Maximum risk-to-capital ratio	25
Adjusted statutory net income measurement period			3 years
Adjusted statutory net income dividend payment measurement period			2 years
Reduction in statutory net income due to increase in contingency reserve				$ 444