XML 107 R79.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Litigation and Contingencies (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract] |  |
Average paid claim reduction due to curtailments (in hundredths) | 5.60% | 5.50%
Maximum exposure to loss | $ 285 |

X
- Definition Average paid claim reduction due to curtailments. + References No definition available. + Details
Name: | mtg_AveragePaidClaimsReductionDueToCurtailments
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated maximum exposure associated with other discussions and legal proceedings related to claims paying practices. + References No definition available. + Details
Name: | mtg_MaximumExposureAssociatedWithOtherDiscussionsLegalProceedings
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration