Concentrations of Credit Risk Geographic Concentration (Details) - Guaranty Book of Business - Geographic Concentration Risk	Dec. 31, 2023	Dec. 31, 2022
Single-family
Concentration Risk [Line Items]
Percentage of book of business	100.00%	100.00%
Single-family | Midwest
Concentration Risk [Line Items]
Percentage of book of business	14.00%	14.00%
Single-family | Northeast
Concentration Risk [Line Items]
Percentage of book of business	16.00%	16.00%
Single-family | Southeast
Concentration Risk [Line Items]
Percentage of book of business	23.00%	23.00%
Single-family | Southwest
Concentration Risk [Line Items]
Percentage of book of business	19.00%	19.00%
Single-family | West
Concentration Risk [Line Items]
Percentage of book of business	28.00%	28.00%
Multifamily
Concentration Risk [Line Items]
Percentage of book of business	100.00%	100.00%
Multifamily | Midwest
Concentration Risk [Line Items]
Percentage of book of business	12.00%	12.00%
Multifamily | Northeast
Concentration Risk [Line Items]
Percentage of book of business	15.00%	15.00%
Multifamily | Southeast
Concentration Risk [Line Items]
Percentage of book of business	27.00%	27.00%
Multifamily | Southwest
Concentration Risk [Line Items]
Percentage of book of business	22.00%	22.00%
Multifamily | West
Concentration Risk [Line Items]
Percentage of book of business	24.00%	24.00%