Reinsurance - QSR Program (Details) - Radian Guaranty - USD ($) $ in Millions	Jul. 01, 2024	Jul. 01, 2023	Jul. 01, 2022	Jan. 01, 2020	Jan. 01, 2018	Jan. 01, 2016	Sep. 30, 2024	Dec. 31, 2023
2024 QSR Agreement
Ceded Credit Risk [Line Items]
Ceding commission %	20.00%
RIF ceded							$ 834	$ 0
2024 QSR Agreement | Revenue Benchmark | Product Concentration Risk
Ceded Credit Risk [Line Items]
Quota share %	25.00%
2023 QSR Agreement
Ceded Credit Risk [Line Items]
Ceding commission %		20.00%
RIF ceded							2,638	1,366
2023 QSR Agreement | Revenue Benchmark | Product Concentration Risk
Ceded Credit Risk [Line Items]
Quota share %		22.50%
2022 QSR Agreement
Ceded Credit Risk [Line Items]
Ceding commission %			20.00%
RIF ceded							4,178	4,454
2022 QSR Agreement | Revenue Benchmark | Product Concentration Risk
Ceded Credit Risk [Line Items]
Quota share %			20.00%
2020 Single Premium QSR Agreement
Ceded Credit Risk [Line Items]
Ceding commission %				25.00%
RIF ceded							1,587	1,783
2020 Single Premium QSR Agreement | Revenue Benchmark | Product Concentration Risk
Ceded Credit Risk [Line Items]
Quota share %				65.00%
2018 Single Premium QSR Agreement
Ceded Credit Risk [Line Items]
Ceding commission %					25.00%
RIF ceded							680	739
2018 Single Premium QSR Agreement | Revenue Benchmark | Product Concentration Risk
Ceded Credit Risk [Line Items]
Quota share %					65.00%
2016 Single Premium QSR Agreement
Ceded Credit Risk [Line Items]
Ceding commission %						25.00%
RIF ceded							$ 904	$ 982
Minimum | 2016 Single Premium QSR Agreement | Revenue Benchmark | Product Concentration Risk
Ceded Credit Risk [Line Items]
Quota share %						18.00%
Maximum | 2024 QSR Agreement
Ceded Credit Risk [Line Items]
Profit commission %	59.00%
Maximum | 2023 QSR Agreement
Ceded Credit Risk [Line Items]
Profit commission %		55.00%
Maximum | 2022 QSR Agreement
Ceded Credit Risk [Line Items]
Profit commission %			59.00%
Maximum | 2020 Single Premium QSR Agreement
Ceded Credit Risk [Line Items]
Profit commission %				56.00%
Maximum | 2018 Single Premium QSR Agreement
Ceded Credit Risk [Line Items]
Profit commission %					56.00%
Maximum | 2016 Single Premium QSR Agreement
Ceded Credit Risk [Line Items]
Profit commission %						55.00%
Maximum | 2016 Single Premium QSR Agreement | Revenue Benchmark | Product Concentration Risk
Ceded Credit Risk [Line Items]
Quota share %						57.00%