Capital Requirements (Details) $ in Millions	3 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) jurisdiction	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) 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				12.6 to 1
Risk-to-capital ratio for combined insurance operations	12.6			12.6
Percentage of statutory policyholders surplus used to determine maximum allowable dividends	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				11.1 to 1
Risk-to-capital ratio	11.1			11.1
Amount of policyholders position above or below required MPP	$ 1,400			$ 1,400
Amount of required MPP	1,100			$ 1,100
Cash dividends paid	$ 16	$ 16	$ 16
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