Description of Business - Mortgage Insurance (Details) - Mortgage Insurance - USD ($) $ in Billions	Dec. 31, 2023	Dec. 31, 2022
Business Overview [Abstract]
Down payment percent of purchase price	20.00%
Equity in home (percent)	20.00%
Direct primary mortgage insurance in force	$ 270.0	$ 261.0
Direct primary mortgage insurance risk in force	$ 69.7	$ 66.1