Reinsurance - Additional Information (Details) - Radian Guaranty $ in Millions		12 Months Ended
		Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Ceded Credit Risk [Line Items]
Funds held under reinsurance agreements, asset		$ 416	$ 283
Excess-of-Loss Program
Ceded Credit Risk [Line Items]
Reinsurance optional clean-up call, outstanding principal balance percentage threshold		0.10
2024 QSR Agreement [Member]
Ceded Credit Risk [Line Items]
RIF ceded	[1]	$ 2,819	$ 1,621
Maximum | Mortgage insurance
Ceded Credit Risk [Line Items]
Reinsurance retention policy, term of coverage, period		12 years 6 months
Maximum | Excess-of-Loss Program
Ceded Credit Risk [Line Items]
Right to termination on or after option call date, period after issuance of insurance-linked notes		7 years
Minimum | Mortgage insurance
Ceded Credit Risk [Line Items]
Reinsurance retention policy, term of coverage, period		10 years
Minimum | Excess-of-Loss Program
Ceded Credit Risk [Line Items]
Right to termination on or after option call date, period after issuance of insurance-linked notes		5 years

[1] Excludes the 2012 QSR Agreements, for which RIF ceded is no longer material, and the 2026 and 2027 QSR Agreements that were entered into in July 2025, but are effective for future NIW vintages from July 1, 2026, to June 30, 2027, and July 1, 2027, to June 30, 2028, respectively, with cessions of 30% and 15%, respectively.