Abu Dhabi Commercial Bank Litigation [Member] Abu Dhabi Commercial Bank Litigation [Member] Abu Dhabi Commercial Bank Litigation Accounts Payable And Accrued Liabilities Current Accounts payable and accrued liabilities Total accounts payable and accrued liabilities Accounts Payable And Accrued Liabilities Current And Noncurrent [Abstract] Accounts payable and accrued liabilities: Accounts Payable and Accrued Liabilities [Member] Accounts Payable And Accrued Liabilities [Member] Accounts payable and accrued liabilities Accounts Payable Current Accounts payable Accounts Receivable Net Current Accounts receivable, net of allowances of $30.0 in 2012 and $28.0 in 2011 Accrued Bonuses Current And Noncurrent Incentive compensation Accrued Income Taxes Current Income taxes Accrued Professional Fees Current Professional service fees Accumulated Depreciation Depletion And Amortization Property Plant And Equipment Property and equipment, accumulated depreciation Accumulated change, net of tax, in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow and net investment hedges. Accumulated Other Comprehensive Income Loss Cumulative Changes In Net Gain Loss From Hedging Activities Effect Net Of Tax Cumulative amount of unrecognized hedge losses recorded in AOCI Unrealized losses on cash flow and net investment hedges, net of tax Accumulated Other Comprehensive Income Loss Defined Benefit Pension And Other Postretirement Plans Net Of Tax Net actuarial losses and net prior service cost related to Post-retirement plans, net of tax Accumulated Other Comprehensive Income Loss Foreign Currency Translation Adjustment Net Of Tax Currency translation adjustments, net of tax Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income Loss [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income Loss Net Of Tax Accumulated other comprehensive loss Total accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income Loss [Table] Accumulated Other Comprehensive Income (Loss) [Table] Acquired Finite Lived Intangible Assets Weighted Average Useful Life Weighted average life of intangible assets acquired (in years) Additional Financial Information Disclosure [Text Block] OTHER BALANCE SHEET INFORMATION Additional Paid In Capital Common Stock Capital surplus Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Reconciliation of net income to net cash provided by operating activities: Allowance For Doubtful Accounts Receivable Current Accounts receivable, allowances Amendment Flag Amendment Flag Amortization Of Intangible Assets Amortization expense Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Anti-dilutive options to purchase common shares and restricted stock excluded from the table above Applicable margin on LIBOR-based borrowings of the Company. Applicable Margin Rate On London Interbank Offered Rate Rate Interest rate, LIBOR marginal basis points Assets Total Assets Total assets Assets [Abstract] ASSETS Assets Current Total current assets Assets Current [Abstract] Current assets: Assets Fair Value Disclosure Total, assets Maximum amount, under a proposed settlement for which the Company has agreed not to oppose an application for attorney's fees and costs. Attorneys Fees And Costs Agreed Not To Oppose Loss related to application for attorney's fees and costs, maximum amount Award Type [Axis] Award Type [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Barrie Hibbert Limited [Member] Barrie Hibbert Limited [Member] Barrie & Hibbert Limited Business Acquisition Acquiree [Domain] Business Acquisition, Acquiree [Domain] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition Contingent Consideration At Fair Value Contingent consideration arising from acquisitions, liabilities Contingent consideration at fair value Amount of contingent consideration in accounts payable and accrued liabilities at the balance sheet date. Business Acquisition Contingent Consideration Obligations Accounts Payable And Accrued Liabilities Business acquisition contingent consideration obligations, accounts payable and accrued liabilities Amount of contingent consideration in other liabilities as of the balance sheet date. Business Acquisition Contingent Consideration Obligations Other Liabilities Business acquisition contingent consideration obligations, other liabilities Business Acquisition Contingent Consideration Potential Cash Payment Contingent payment Business Acquisition Cost Of Acquired Entity Cash Paid Cash paid Business Acquisition Cost Of Acquired Entity Liabilities Incurred Contingent consideration liability assumed Contingent consideration liability assumed, Copal Business Acquisition Cost Of Acquired Entity Purchase Price Purchase price Business Acquisition Cost Of Acquired Entity Transaction Costs Amount related to transaction cost Business Acquisition [Line Items] Business Acquisition [Line Items] Business Acquisition Percentage Of Voting Interests Acquired Additional direct equity investment in KIS pricing Business Acquisition Purchase Price Allocation Amortizable Intangible Assets Total intangible assets Business Acquisition Purchase Price Allocation Assets Acquired Liabilities Assumed Net Net assets acquired Business Acquisition Purchase Price Allocation Current Assets Current assets Business Acquisition Purchase Price Allocation Goodwill Amount Goodwill Business Acquisition Purchase Price Allocation Liabilities Assumed Liabilities assumed Business Acquisition Purchase Price Allocation Noncurrent Assets Other assets Business Acquisition Purchase Price Allocation Property Plant And Equipment Property and equipment, net Business Combination Consideration Transferred Including Equity Interest In Acquiree Held Prior To Combination Total fair value of consideration transferred Business Combination Consideration Transferred Other Put/call option for non-controlling interest Business Combination Disclosure [Text Block] ACQUISITIONS Business Combination Indemnification Assets Amount As Of Acquisition Date Indemnification asset Cash Acquired From Acquisition Acquired cash Cash And Cash Equivalents At Carrying Value Cash and cash equivalents, end of the period Cash and cash equivalents, beginning of the period Cash and cash equivalents Cash And Cash Equivalents Period Increase Decrease Net increase in cash and cash equivalents Cash Flow Hedging [Member] Cash Flow Hedging Class Action [Member] Class Action [Member] King County, Washington and Iowa Student Loan Liquidity Corporation Class Of Stock [Domain] Class of Stock [Domain] Commercial Paper Commercial paper Commercial Paper [Member] Commercial Paper Commitments And Contingencies Contingencies (Note 14) Commitments And Contingencies Disclosure [Text Block] CONTINGENCIES Common Stock Dividends Per Share Declared Dividends declared per share attributable to Moody's common shareholders Common Stock [Member] Common Stock Common Stock Par Or Stated Value Per Share Common stock, par value Common Stock Shares Authorized Common stock, shares authorized Common Stock Shares Issued Common stock, shares issued Common Stock Shares Outstanding Common stock, shares outstanding Common Stock Value Common stock Compensation Related Costs Share Based Payments Disclosure [Line Items] Compensation Related Costs Share Based Payments Disclosure [Line Items] Compensation Related Costs Share Based Payments Disclosure [Line Items] Component Of Other Expense Income Nonoperating [Axis] Component Of Other Expense Income Nonoperating [Axis] Component Of Other Expense Income Nonoperating [Axis] Component Of Other Expense Income Nonoperating [Domain] Component Of Other Expense Income Nonoperating [Domain] Component Of Other Expense Income Nonoperating [Domain] Component Of Other Expense Income Nonoperating [Line Items] Component Of Other Expense Income Nonoperating [Line Items] Component Of Other Expense Income Nonoperating [Line Items] Component Of Other Expense Income Nonoperating [Table] Component Of Other Expense Income Nonoperating [Table] Component Of Other Expense Income Nonoperating [Table] Comprehensive Income Net Of Tax Comprehensive income attributable to Moody's Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest Less: comprehensive income attributable to noncontrolling interests Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest Comprehensive income Copal Group Of Companies [Member] Copal Group Of Companies [Member] Copal Group Of Companies Copal [Member] Copal [Member] Copal Copal Partners [Member] Copal Partners [Member] Copal Partners Consists of revenue relating to the rating and monitoring of debt issued by commercial and industrial corporations. Corporate Finance [Member] Corporate finance (CFG) Corporate [Member] Corporate Current Fiscal Year End Date Current Fiscal Year End Date Carrying amount, as of the balance sheet date, for customer credits, payments received in advance of billings and billings in advance of services being rendered or products being delivered. Customer Billings And Payments Received In Advance Customer credits, advanced payments and advanced billings Customer Relationships [Member] Client relationships Debt And Capital Lease Obligations Total debt Debt Current Current portion Debt Disclosure [Text Block] INDEBTEDNESS Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument Call Feature Prepayment and purchase feature of Senior Unsecured Notes Debt Instrument Carrying Amount Carrying Amount Debt Instrument Convertible Conversion Ratio Debt to EBITDA ratio Debt Instrument Covenant Description Debt to EBITDA ratio not to exceed at the end of any fiscal quarter Debt Instrument Covenant, Permitted Interest Ratio Debt Instrument Covenant Permitted Interest Ratio Debt to EBITDA ratio Debt Instrument Face Amount Debt, aggregate principal amount Debt Instrument Fair Value Estimated Fair Value Debt Instrument Fee Quarterly facility fees Debt Instrument Interest Rate Stated Percentage Senior Unsecured Notes, interest Debt Instrument Interest Rate Terms Interest on borrowings under Term Loan Debt Instrument Issuance Date 1 Date of agreement with the lenders for the five year senior unsecured term loan Debt Instrument [Line Items] Debt Instrument [Line Items] Debt Instrument Maturity Date Maturity date of Senior Unsecured Notes Debt Instrument Maturity Date Description Maturity date of CP Notes (in days) Debt Instrument Name [Domain] Debt Instrument, Name [Domain] Debt Instrument Restrictive Covenants Minimum percentage for default on senior notes payable Number of years until maturity for certain of the company's long and short-term borrowing arrangements. Debt Instruments Maturity Duration Debt instrument term (in years) Debt Instrument [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument Unamortized Discount Unamortized discount Debt Instrument Unused Borrowing Capacity Amount Issuance of additional principal amount of Senior Notes within five years from time to time Fee charged to the Company on borrowings outstanding when the aggregate amount outstanding on the credit facility exceeds 50% of the total facility. Debt Instrument Utilization Fee Description Utilization fee Deferred Income Tax Expense Benefit Deferred income taxes Deferred Rent Credit Current Deferred rent-current portion Deferred Rent Credit Noncurrent Deferred rent-non-current portion Deferred Revenue Current Deferred revenue Deferred Revenue Noncurrent Non-current portion of deferred revenue Deferred Tax Assets Net Current Deferred tax assets, net Deferred Tax Assets Net Noncurrent Deferred tax assets, net Deferred Tax Liabilities Noncurrent Deferred tax liabilities, net Defined Benefit Plan Amortization Of Gains Losses Amortization of net actuarial loss from earlier periods Defined Benefit Plan Benefits Paid Defined benefit payment amount Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Estimated Future Employer Contributions In Current Fiscal Year Estimated additional payments in 2012 Defined Benefit Plan Expected Return On Plan Assets Expected return on plan assets Defined Benefit Plan Interest Cost Interest cost Defined Benefit Plan Net Periodic Benefit Cost Net periodic expense Defined Benefit Plan Recognized Net Gain Loss Due To Settlements 1 Settlement loss Defined Benefit Plans And Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans Disclosures Defined Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans [Domain] Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Defined Benefit Plan Service Cost Service cost Deposit Assets Deposits for real-estate leases Depreciation And Amortization Depreciation and amortization Derivative Assets Derivatives, assets Derivative By Nature [Axis] Derivative, by Nature [Axis] Derivative Contract Type [Domain] Derivative Contract Type [Domain] Derivative Description Of Variable Rate Basis Floating interest rate base Derivative Fair Value Of Derivative Asset Derivatives assets Fair value of interest rate swap Derivative Fair Value Of Derivative Liability Derivatives liabilities Derivative Financial Instruments Liabilities Fair Value Disclosure Derivatives, liabilities Derivative Instrument Risk [Axis] Derivative Instrument Risk [Axis] Derivative Instruments And Hedging Activities Disclosure [Text Block] DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES Derivative Instruments Gain Loss By Hedging Relationship [Axis] Hedging Relationship [Axis] Derivative Instruments Gain Loss By Hedging Relationship By Income Statement Location By Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments Gain Loss [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments Gain Loss Reclassified From Accumulated O C I Into Income Effective Portion Net Amount of Gain/(Loss) Reclassified from AOCI into Income (Effective Portion) Derivative Instruments Gain Loss Recognized In Income Ineffective Portion And Amount Excluded From Effectiveness Testing Net Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing) Derivative Instruments Gain Loss Recognized In Income Net Amount of Gain (Loss) Recognized in Income Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net Amount of Gain/(Loss) Recognized in AOCI on Derivative (Effective Portion) Derivative [Line Items] Derivative [Line Items] Derivative Name [Domain] Derivative, Name [Domain] Derivatives Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative [Table] Derivative [Table] Designated As Hedging Instrument [Member] Derivatives designated as accounting hedges Direct Operating Costs Operating The total of direct operating costs and costs related to selling the Company's products and services, as well as all other general and administrative expenses. Direct selling expenses are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc. Direct Operating Costs Selling General And Administrative Expense Operating, SG&A Disclosure - Acquired Intangible Assets and Related Amortization [Abstract] Disclosure Acquired Intangible Assets And Related Amortization [Abstract] Disclosure - Acquired Intangible Assets and Related Amortization [Abstract] Disclosure Acquisitions Additional Information [Abstract] Disclosure Acquisitions Additional Information [Abstract] Disclosure Acquisitions Additional Information [Abstract] Disclosure - Activity in Goodwill [Abstract] Disclosure Activity In Goodwill [Abstract] Disclosure - Activity in Goodwill [Abstract] Disclosure - Additional Details Related to Certain Balance Sheet Captions [Abstract] Disclosure Additional Details Related To Certain Balance Sheet Captions [Abstract] Disclosure - Additional Details Related to Certain Balance Sheet Captions [Abstract] Disclosure - Amortization Expense Relating to Acquired Intangible Assets [Abstract] Disclosure Amortization Expense Relating To Acquired Intangible Assets [Abstract] Disclosure - Amortization Expense Relating to Acquired Intangible Assets [Abstract] Disclosure - Barrie and Hibbert, Limited, Purchase Price Allocation [Abstract] Disclosure Barrie And Hibbert Limited Purchase Price Allocation [Abstract] Disclosure - Barrie and Hibbert, Limited, Purchase Price Allocation [Abstract] Disclosure - Cash Paid for Interest [Abstract] Disclosure Cash Paid For Interest [Abstract] Disclosure - Cash Paid for Interest [Abstract] Disclosure - Changes in Fair Value of Level 3 Liabilities, Contingent Consideration [Abstract] Disclosure Changes In Fair Value Of Level 3 Liabilities Contingent Consideration [Abstract] Disclosure - Changes in Fair Value of Level 3 Liabilities, Contingent Consideration [Abstract] Disclosure - Changes in Non-Redeemable Noncontrolling Interest [Abstract] Disclosure Changes In Non Redeemable Noncontrolling Interest [Abstract] Disclosure - Changes in Non-Redeemable Noncontrolling Interest [Abstract] Disclosure - Changes in Redeemable Noncontrolling Interest Related to Acquisition [Abstract] Disclosure Changes In Redeemable Noncontrolling Interest Related To Acquisition [Abstract] Disclosure - Changes in Redeemable Noncontrolling Interest Related to Acquisition [Abstract] Disclosure - Components of Accumulated Other Comprehensive Income [Abstract] Disclosure Components Of Accumulated Other Comprehensive Income [Abstract] Disclosure - Components of Accumulated Other Comprehensive Income [Abstract] Disclosure - Components of Net Periodic Benefit Expense Related to Retirement Plans [Abstract] Disclosure Components Of Net Periodic Benefit Expense Related To Retirement Plans [Abstract] Disclosure - Components of Net Periodic Benefit Expense Related to Retirement Plans [Abstract] Disclosure - Components of Other Non-Operating (Expense) Income [Abstract] Disclosure Components Of Other Non Operating Expense Income [Abstract] Disclosure - Components of Other Non-Operating (Expense) Income [Abstract] Disclosure - Consolidated Revenue Information by Geographic Area [Abstract] Disclosure Consolidated Revenue Information By Geographic Area [Abstract] Disclosure - Consolidated Revenue Information by Geographic Area [Abstract] Disclosure Contingencies Additional Information [Abstract] Disclosure Contingencies Additional Information [Abstract] Disclosure Contingencies Additional Information [Abstract] Disclosure - Copal Partners, Purchase Price Allocation [Abstract] Disclosure Copal Partners Purchase Price Allocation [Abstract] Disclosure - Copal Partners, Purchase Price Allocation [Abstract] Disclosure - Copal Partners, Total Consideration Transferred to Sellers [Abstract] Disclosure Copal Partners Total Consideration Transferred To Sellers [Abstract] Disclosure - Copal Partners, Total Consideration Transferred to Sellers [Abstract] Disclosure - Cumulative Amount of Unrecognized Hedge Losses Recorded in Accumulated Other Comprehensive Income [Abstract] Disclosure Cumulative Amount Of Unrecognized Hedge Losses Recorded In Accumulated Other Comprehensive Income [Abstract] Disclosure - Cumulative Amount of Unrecognized Hedge Losses Recorded in Accumulated Other Comprehensive Income [Abstract] Disclosure Derivative Instrumentsand Hedging Activities Additional Information [Abstract] Disclosure Derivative Instrumentsand Hedging Activities Additional Information [Abstract] Disclosure Derivative Instrumentsand Hedging Activities Additional Information [Abstract] Disclosure - Description of Business and Basis of Presentation - Additional Information [Abstract] Disclosure Description Of Business And Basis Of Presentation Additional Information [Abstract] Disclosure - Description of Business and Basis of Presentation - Additional Information [Abstract] Disclosure - Estimated Future Amortization Expense for Acquired Intangible Assets Subject to Amortization [Abstract] Disclosure Estimated Future Amortization Expense For Acquired Intangible Assets Subject To Amortization [Abstract] Disclosure - Estimated Future Amortization Expense for Acquired Intangible Assets Subject to Amortization [Abstract] Disclosure Fair Value Additional Information [Abstract] Disclosure Fair Value Additional Information [Abstract] Disclosure Fair Value Additional Information [Abstract] Disclosure - Fair Value and Carrying Value of Long-Term Debt [Abstract] Disclosure Fair Value And Carrying Value Of Long Term Debt [Abstract] Disclosure - Fair Value and Carrying Value of Long-Term Debt [Abstract] Disclosure - Fair Value of Derivative Instruments [Abstract] Disclosure Fair Value Of Derivative Instruments [Abstract] Disclosure - Fair Value of Derivative Instruments [Abstract] Disclosure - Financial Information by Segment [Abstract] Disclosure Financial Information By Segment [Abstract] Disclosure - Financial Information by Segment [Abstract] Disclosure - Financial Instruments Carried at Fair Value on Recurring Basis [Abstract] Disclosure Financial Instruments Carried At Fair Value On Recurring Basis [Abstract] Disclosure - Financial Instruments Carried at Fair Value on Recurring Basis [Abstract] Disclosure - Gains and Losses on Derivatives Designated as Hedging Instruments, Cash Flow Hedging [Abstract] Disclosure Gains And Losses On Derivatives Designated As Hedging Instruments Cash Flow Hedging [Abstract] Disclosure - Gains and Losses on Derivatives Designated as Hedging Instruments, Cash Flow Hedging [Abstract] Disclosure - Gains and Losses on Derivatives Designated as Hedging Instruments, Net Investment Hedging [Abstract] Disclosure Gains And Losses On Derivatives Designated As Hedging Instruments Net Investment Hedging [Abstract] Disclosure - Gains and Losses on Derivatives Designated as Hedging Instruments, Net Investment Hedging [Abstract] Disclosure - Goodwill and Other Acquired Intangible Assets - Additional Information [Abstract] Disclosure Goodwill And Other Acquired Intangible Assets Additional Information [Abstract] Disclosure - Goodwill and Other Acquired Intangible Assets - Additional Information [Abstract] Disclosure Income Taxes Additional Information [Abstract] Disclosure Income Taxes Additional Information [Abstract] Disclosure Income Taxes Additional Information [Abstract] Disclosure - Income Taxes Paid [Abstract] Disclosure Income Taxes Paid [Abstract] Disclosure - Income Taxes Paid [Abstract] Disclosure - Indebtedness - Additional Information [Abstract] Disclosure Indebtedness Additional Information [Abstract] Disclosure - Indebtedness - Additional Information [Abstract] Disclosure Of Compensation Related Costs Share Based Payments [Text Block] STOCK-BASED COMPENSATION Disclosure Of Share Based Compensation Arrangements By Share Based Payment Award [Text Block] Stock-Based Compensation Cost and Associated Tax Benefit Disclosure - Pension and Other Retirement Benefits - Additional Information [Abstract] Disclosure Pension And Other Retirement Benefits Additional Information [Abstract] Disclosure - Pension and Other Retirement Benefits - Additional Information [Abstract]