XML 82 R58.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Statutory Information (Details) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2018 USD ($) jurisdiction | Sep. 30, 2018 USD ($) jurisdiction | Dec. 31, 2017 USD ($)
Statutory capital requirements [Abstract] |  |  |
Number of jurisdictions with risk-to-capital requirements (in jurisdictions) | jurisdiction | 16 | 16 |
Maximum permitted risk-to-capital ratio commonly applied |  | 25 to 1 |
Risk to capital ratio of combined insurance operations, including reinsurance affiliates, at end of period |  | 9.8 to 1 |
Risk-to-capital ratio for combined insurance operations | 9.8 | 9.8 |
Percentage of statutory policyholders surplus used to determine maximum allowable dividends (as a percent) | 10.00% | 10.00% |
Mortgage Guaranty Insurance Corporation |  |  |
Statutory capital requirements [Abstract] |  |  |
Maximum risk-to-capital ratio |  | 25 |
Risk to capital ratio at end of period |  | 9.0 to 1 |
Risk-to-capital ratio | 9.0 | 9.0 |
Amount of policyholders position above or below required MPP | $ 2,500 | $ 2,500 |
Amount of required MPP | 1,300 | $ 1,300 |
Dividends paid to the parent company | $ 60 |  |
Adjusted statutory net income measurement period (in years) |  | 3 years |
Adjusted statutory net income dividend payment measurement period (in years) |  | 2 years |
Reduction in statutory net income due to increase in contingency reserve |  |  | $ 473
Statutory net income |  |  | $ 272

X
- Definition The amount by which the entity's policyholders position (the insurer's net worth or surplus, contingency reserve and a portion of the reserves for unearned premiums) was above or below the required regulatory minimum of the entity's domiciliary state. + References No definition available. + Details
Name: | mtg_AmountOfPolicyholdersPositionAboveOrBelowRequiredRegulatoryMinimum
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The amount of minimum policyholder position (MPP) required by the entity's domiciliary state. + References No definition available. + Details
Name: | mtg_AmountOfRequiredMpp
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The number of jurisdictions that require a mortgage insurer to maintain a minimum amount of statutory capital relative to the risk in force (or a similar measure) in order for the mortgage insurer to continue to write new business. This is generally referred to as a risk-to-capital requirement. + References No definition available. + Details
Name: | mtg_NumberOfJurisdictionsWithRiskToCapitalRequirements
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of statutory policyholders' surplus, as defined, as of the preceding calendar year end which is used in the determination of the maximum allowable dividends that the insurance subsidiaries may pay in any twelve-month period without regulatory approval by the Office of the Commissioner of Insurance of the State of Wisconsin. + References No definition available. + Details
Name: | mtg_PercentageOfStatutoryPolicyholdersSurplusUsedToDetermineMaximumAllowableDividends
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The entity's risk-to-capital ratio as of the end of the reporting period. + References No definition available. + Details
Name: | mtg_Risktocapitalratioatendofperiod
Namespace Prefix: | mtg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The risk-to-capital ratio of the entity's combined insurance operations, including its reinsurance affiliates, as of the end of the reporting period. + References No definition available. + Details
Name: | mtg_Risktocapitalratioofcombinedinsuranceoperationsincludingreinsuranceaffiliatesatendofperiod
Namespace Prefix: | mtg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Statutory Accounting Practices, Regulatory Capital Requirements, Risk-to-Capital Ratio, Maximum + References No definition available. + Details
Name: | mtg_StatutoryAccountingPracticesRegulatoryCapitalRequirementsRisktoCapitalRatioMaximum
Namespace Prefix: | mtg_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Statutory Accounting Practices, Statutory Amount Available For Dividend Payments Without Regulatory Approval, Measurement, Measurement Period + References No definition available. + Details
Name: | mtg_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApprovalMeasurementMeasurementPeriod
Namespace Prefix: | mtg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval, Measurement, Dividend Payment Period + References No definition available. + Details
Name: | mtg_StatutoryAccountingPracticesStatutoryAmountAvailableforDividendPaymentswithoutRegulatoryApprovalMeasurementDividendPaymentPeriod
Namespace Prefix: | mtg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Statutory Accounting Practices, Statutory Net Income, Adjustment + References No definition available. + Details
Name: | mtg_StatutoryAccountingPracticesStatutoryNetIncomeAdjustment
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Definition Statutory Capital Requirements, Risk To Capital Ratio + References No definition available. + Details
Name: | mtg_StatutoryCapitalRequirementsRiskToCapitalRatio
Namespace Prefix: | mtg_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition Statutory Capital Requirements, Risk To Capital Ratio For Combined Insurance Operations + References No definition available. + Details
Name: | mtg_StatutoryCapitalRequirementsRiskToCapitalRatioForCombinedInsuranceOperations
Namespace Prefix: | mtg_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents disclosure of the total aggregate cash dividends paid to the entity by consolidated subsidiaries, by unconsolidated subsidiaries, and by 50% or less owned persons accounted for using the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(b)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.9-06) -URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537971-122884 + Details
Name: | us-gaap_CashDividendsPaidToParentCompany
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition For insurance companies, a description of the minimum regulatory capital requirements imposed by state insurance regulators, and restrictions on dividend payments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 505 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529 + Details
Name: | us-gaap_DescriptionOfRegulatoryCapitalRequirementsUnderInsuranceRegulations
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(23)(c)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
Name: | us-gaap_StatutoryAccountingPracticesStatutoryNetIncomeAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=mtg_MortgageGuarantyInsuranceCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |