Description of Business - Mortgage (Details) - Mortgage - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Business Overview [Abstract]
Down payment percent of purchase price	20.00%
Equity in home (percent)	20.00%
Direct primary mortgage insurance in force	$ 246,000.0	$ 246,100.0
Direct primary mortgage insurance risk in force	60,900.0	60,700.0
Credit Risk Transfer Transactions
Business Overview [Abstract]
Direct primary mortgage insurance risk in force	$ 417.7	$ 392.0