Summary of Significant Accounting Policies Regulatory Matters (Details) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2020 USD ($) jurisdiction	Dec. 31, 2014 USD ($)	Jun. 30, 2014	Jun. 30, 2012
Loss Contingencies [Line Items]
Number of Jurisdictions | jurisdiction		16
Mortgage Guaranty Insurers' Contingency Reserves		$ 316.7
RFIG Run-off Business [Member]
Loss Contingencies [Line Items]
Risk to Capital Ratio		25
Percentage of Claims To Be Paid In Cash				100.00%
Proceeds from Contributions from Parent			$ 125.0
Deferred Payment Obligation, Percentage					40.00%
Deferred Payment Obligation	$ 657.0
Statutory Capital		$ 435.2
Amount Above Minimum Policyholder Position		363.7
Minimum Policyholder Position		$ 71.5