Reinsurance - Excess-of-Loss Program (Details) - USD ($) $ in Millions	1 Months Ended					9 Months Ended	12 Months Ended
	Nov. 30, 2021	Apr. 30, 2021	Feb. 29, 2020	Apr. 30, 2019	Nov. 30, 2018	Sep. 30, 2022	Dec. 31, 2021
Mortgage
RIF						$ 65,300.0	$ 60,900.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-2 Ltd. | Mortgage
RIF	$ 10,758.0					9,394.0	10,379.0
Initial and remaining coverage	484.0					484.0	484.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-2 Ltd. | First Layer Retention | Mortgage
Initial first layer retention	$ 242.0					242.0	242.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 Ltd. | Mortgage
RIF		$ 11,061.0				8,223.0	9,496.0
Initial and remaining coverage		498.0				401.0	498.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 Ltd. | Radian Group Inc.
Proceeds from issuance of debt						45.4
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2021-1 Ltd. | First Layer Retention | Mortgage
Initial first layer retention		$ 221.0				221.0	221.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-1 Ltd. | Mortgage
RIF			$ 9,866.0			2,510.0	3,241.0
Initial and remaining coverage			488.0			394.0	488.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2020-1 Ltd. | First Layer Retention | Mortgage
Initial first layer retention			$ 202.0			202.0	202.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2019-1 Ltd. | Mortgage
RIF				$ 10,705.0		1,849.0	2,429.0
Initial and remaining coverage				562.0		385.0	385.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2019-1 Ltd. | First Layer Retention | Mortgage
Initial first layer retention				$ 268.0		263.0	264.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2018-1 Ltd. | Mortgage
RIF					$ 9,109.0	1,596.0	2,117.0
Initial and remaining coverage					434.0	276.0	276.0
Excess-of-Loss Program | Radian Guaranty | Eagle Re 2018-1 Ltd. | First Layer Retention | Mortgage
Initial first layer retention					$ 205.0	$ 201.0	$ 201.0