Related Party Transactions [Abstract] Related Party Transactions [Abstract] Adjustments for Error Corrections [Axis] Adjustments for Error Corrections [Axis] Outstanding Balance Long-term Line of Credit Expected amortization expense, year one Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months Total current liabilities Liabilities, Current Accrued interest Increase (Decrease) in Interest Payable, Net Other services Other services [Member] Other services [Member] Interest cost Defined Benefit Plan, Interest Cost OTHER COMPREHENSIVE INCOME Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Repayments of revolving credit agreements Repayments of Lines of Credit Net cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Current Fiscal Year End Date Current Fiscal Year End Date Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Total operating revenues Revenues Revenue (increase) decrease Operating revenues Revenues Entity Address, Postal Zip Code Entity Address, Postal Zip Code Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount Property, plant and equipment (net of accumulated depreciation and amortization of $2,011 and $1,930, respectively) Property, Plant and Equipment, Net AOCI Attributable to Parent [Member] AOCI Attributable to Parent [Member] TOTAL ASSETS Assets Assets Regulatory Liability [Axis] Regulatory Liability [Axis] Entity Shell Company Entity Shell Company Regulatory liabilities Current regulatory liabilities Current regulatory liability Regulatory Liability, Current Short-term Debt, Weighted Average Interest Rate, at Point in Time Short-term Debt, Weighted Average Interest Rate, at Point in Time Document Type Document Type Debt, Weighted Average Interest Rate Debt, Weighted Average Interest Rate Subsequent Event Subsequent Event [Member] Employee Stock Ownership Plan (ESOP), Plan [Domain] Employee Stock Ownership Plan (ESOP), Plan [Domain] Scenario [Domain] Scenario [Domain] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Current liabilities Liabilities, Current [Abstract] Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Income tax refunds received Proceeds from Income Tax Refunds Effect on net income from 10 basis point reduction in the authorized base return on equity Effect on net income from 10 basis point reduction in the authorized base return on equity Effect on net income from 10 basis point reduction in the authorized base return on equity Schedule of Debt Instruments [Table] Schedule of Debt Instruments [Table] Schedule of Debt Instruments [Table] Financial Instrument [Axis] Financial Instrument [Axis] SEGMENT INFORMATION Segment Reporting Disclosure [Text Block] 2017 Omnibus Plan 2017 Omnibus Plan [Member] 2017 Omnibus Plan [Member] Equity [Abstract] Equity [Abstract] OPERATING REVENUES: Segment Reporting Information, Revenue for Reportable Segment [Abstract] Unused Capacity Line of Credit Facility, Remaining Borrowing Capacity Segment Reporting Information Segment Reporting Information [Line Items] Entity Common Stock, Shares Outstanding Document Quarterly Report Income Tax Authority [Domain] Income Tax Authority [Domain] Commitments and contingent liabilities (Notes 5 and 13) Commitments and Contingencies Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Refundable deposits Contract with Customer, Liability, Noncurrent CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period Cash, Cash Equivalents and Restricted Cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Debt Instrument [Line Items] Debt Instrument [Line Items] First Mortgage Bonds due July 15, 2051 [Member] First Mortgage Bonds due July 15, 2051 [Member] First Mortgage Bonds due July 15, 2051 Class of Stock [Domain] Class of Stock [Domain] Deferred Income Taxes and Other Liabilities, Noncurrent Deferred Income Taxes and Other Liabilities, Noncurrent Consolidation Items [Domain] Consolidation Items [Domain] Defined Contribution Plan, Cost Defined Contribution Plan, Cost Schedule of Goodwill and Intangible Assets [Table] Schedule of Goodwill and Intangible Assets [Table] Schedule of Goodwill and Intangible Assets [Table] Entity File Number Entity File Number Compensation Expense (less than $1 million) Employee Stock Ownership Plan (ESOP), Compensation Expense Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Defined Benefit Plan, Plan Assets, Contributions by Employer Defined Benefit Plan, Plan Assets, Contributions by Employer Other Proceeds from (Payments for) Other Financing Activities Total unrecognized compensation cost Share-based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Document Fiscal Period Focus Document Fiscal Period Focus Financial Instruments [Domain] Financial Instruments [Domain] Other assets Other Assets [Abstract] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Impact from Recognition of Liability [Domain] Impact from Recognition of Liability [Domain] [Domain] for Impact from Recognition of Liability [Axis] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Product and Service [Domain] Product and Service [Domain] Other Long-term Debt Borrowings Under Term Loan Credit Agreement Borrowings Under Term Loan Credit Agreement Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Incentive Adder for Independent Transmission Ownership Incentive Adder for Independent Transmission Ownership Incentive Adder for Independent Transmission Ownership Schedule of Regulatory Liabilities [Table] Schedule of Regulatory Liabilities [Table] Trade accounts receivable Trade Accounts Receivable [Member] Commercial Paper [Member] Commercial Paper [Member] Rate of Return on Equity and Capital Structure Initial Complaint [Member] Rate of Return on Equity and Capital Structure Initial Complaint [Member] Rate of Return on Equity and Capital Structure Initial Complaint [Member] Other Other Receivables OPERATING INCOME Operating Income (Loss) Operating Income (Loss) Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Borrowings under term loan credit agreements Proceeds from Other Debt Transmission Rate, Applicable Period Transmission Rate, Applicable Period Transmission Rate, Applicable Period Other intangible assets Other Intangible Assets, Net Goodwill Goodwill Maximum Annual Contribution Percentage of Pay Employee Stock Ownership Plan (ESOP), Employer Maximum Annual Contribution Percentage of Pay Employer maximum annual contribution as a percentage of an employee's base pay Measurement Frequency [Domain] Measurement Frequency [Domain] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Statement [Line Items] Statement [Line Items] Transmission and other services Revenue from Contract with Customer, Excluding Assessed Tax Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Restatement [Domain] Restatement [Domain] Schedule of Impacts from the Initial and Second ROE Complaints Schedule Of Impacts from the Initial and Second ROE Complaints [Table Text Block] [Table Text Block] for Schedule Of Impacts from the Initial and Second ROE Complaints [Table] Comprehensive Income (Loss), Net of Tax, Attributable to Parent TOTAL COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Attributable to Parent Plan Name [Axis] Plan Name [Axis] Mutual fund - fixed income securities [Member] Mutual fund - fixed income securities [Member] Mutual fund - fixed income securities [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Derivative Asset Derivative Asset, Fair Value, Gross Liability Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Amendment Flag Amendment Flag Public Utilities Regulatory Complaint Proceeding Items [Axis] Public Utilities Regulatory Complaint Proceeding Items [Axis] Public Utilities Regulatory Complaint Proceeding Items [Axis] Changes in assets and liabilities, exclusive of changes shown separately: Increase (Decrease) in Operating Capital [Abstract] INCOME BEFORE INCOME TAXES Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Common stock, shares outstanding Common Stock, Shares, Outstanding Commitments and Contingent Liabilities [Table] Commitments and Contingent Liabilities [Table] Commitments and Contingent Liabilities [Table] Goodwill and Intangible Assets [Line Items] Goodwill and Intangible Assets [Line Items] Goodwill and Intangible Assets [Line Items] Consolidation Items [Axis] Consolidation Items [Axis] Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] Interest expense, net Interest expense (decrease) increase Interest Expense Class of Stock [Axis] Class of Stock [Axis] Plan Name [Domain] Plan Name [Domain] STOCKHOLDER'S EQUITY Stockholders' Equity Note Disclosure [Text Block] GENERAL Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Granted Award Vesting Rights Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights Net revenue accrual for the six months ended June 30, 2020 Net Revenue Accruals (Deferrals) For The Period Net Revenue Accruals (Deferrals) For The Period Local Phone Number Local Phone Number Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Accounts receivable Accounts Receivable, after Allowance for Credit Loss, Current Reduced rate of return on equity Reduced Rate of Return on Equity Reduced Rate of Return on Equity Rate of Return on Equity and Capital Structure Complaints Rate of Return on Equity and Capital Structure Complaints [Member] Rate of Return on Equity and Capital Structure Complaints [Member] Total other expenses (income) Total other expenses (income) Nonoperating Income (Expense) Nonoperating Income (Expense) Prepaid and other current assets Prepaid Expense and Other Assets, Current Net (repayment) issuance of commercial paper Proceeds from (Repayments of) Commercial Paper Reclassification Aof net loss relating to interest rate cash flow hedges from AOCI to earnings, Tax of less than $1 million Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Total current assets Assets, Current Entity Current Reporting Status Entity Current Reporting Status Revenue Deferrals, Including Accrued Interest Revenue Deferrals, Including Accrued Interest [Member] Revenue Deferrals, Including Accrued Interest [Member] New Accounting Pronouncements and Changes in Accounting Principles [Abstract] New Accounting Pronouncements and Changes in Accounting Principles [Abstract] NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect FERC Order [Member] FERC Order [Member] FERC Order [Member] NET INCOME NET INCOME Estimated net income increase (reduction) Net Income (Loss) Attributable to Parent Common Stock [Member] Common Stock [Member] Current assets Assets, Current [Abstract] Expected amortization expense, year five Finite-Lived Intangible Assets, Amortization Expense, Year Five Leases [Abstract] Leases [Abstract] Debt Instrument [Axis] Debt Instrument [Axis] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Restricted Cash, included in other non-current assets Restricted Cash, Noncurrent Mutual funds Equity Securities, FV-NI Public Utilities Regulatory Complaint Proceeding Items [Domain] Public Utilities Regulatory Complaint Proceeding Items [Domain] [Domain] for Public Utilities Regulatory Complaint Proceeding Items [Axis] Commitments and Contingent Liabilities [Line Items] Commitments and Contingent Liabilities [Line Items] Commitments and Contingent Liabilities [Line Items] Product and Service [Axis] Product and Service [Axis] Supplemental Employee Retirement Plan [Member] Supplemental Employee Retirement Plan [Member] Entity Small Business Entity Small Business Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Scenario [Axis] Scenario [Axis] Entity Filer Category Entity Filer Category ITC Holdings and other Corporate, Non-Segment [Member] Interest Rate Swap [Member] Interest Rate Swap [Member] TOTAL LIABILITIES AND STOCKHOLDER’S EQUITY Liabilities and Equity Entity Address, City or Town Entity Address, City or Town Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Gain (Loss) on Sale of Derivatives Gain (Loss) on Sale of Derivatives Gain (Loss) on Sale of Derivatives Regulatory Asset [Axis] Regulatory Asset [Axis] Receivable Type [Axis] Receivable Type [Axis] Debt maturing within one year Long-term Debt, Current Maturities Impact from Recognition of Liability [Axis] Impact from Recognition of Liability [Axis] Impact from Recognition of Liability [Axis] OPERATING EXPENSES Operating Expenses [Abstract] Adjustments for Error Correction [Domain] Adjustments for Error Correction [Domain] Adjustments for Change in Accounting Principle [Domain] Adjustments for Change in Accounting Principle [Domain] Total available capacity Line of Credit Facility, Current Borrowing Capacity Unsecured Debt [Member] Unsecured Debt [Member] STOCKHOLDER’S EQUITY Stockholders' Equity Attributable to Parent [Abstract] Document Fiscal Year Focus Document Fiscal Year Focus Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Estimated Potential Refund Related to Return on Equity Complaints Estimated Refund Related to Return on Equity Complaint [Member] Estimated Refund Related to Return on Equity Complaint [Member] Pension and Other Postretirement Benefits Disclosure Pension and Other Postretirement Benefits Disclosure [Text Block] SUPPLEMENTAL FINANCIAL INFORMATION Cash Flow, Supplemental Disclosures [Text Block] GENERAL [Abstract] GENERAL [Abstract] GENERAL [Abstract] OPERATING REVENUES Revenues [Abstract] Regulatory Liability [Domain] Regulatory Liability [Domain] Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Fair Value, Recurring [Member] Fair Value, Recurring [Member] Proceeds from (Repayments of) Debt, Maturing in More than Three Months Proceeds from (Repayments of) Debt, Maturing in More than Three Months Award Type [Axis] Award Type [Axis] Intercompany eliminations Consolidation, Eliminations [Member] INCOME (LOSS) BEFORE INCOME TAXES: Segment Reporting Information, Income (Loss) before Income Taxes [Abstract] Accrued taxes Increase (Decrease) in Accrued Taxes Payable Other (income) and expenses, net Other Nonoperating Income (Expense) Other Nonoperating Income (Expense) Related Party Transactions Disclosure Related Party Transactions Disclosure [Text Block] Accumulated other comprehensive (loss) income Balance at the beginning of period Balance at the end of period Accumulated Other Comprehensive Income (Loss), Net of Tax Formula rate true-up Formula Rate True-Up Revenue The true-up mechanism under our Formula Rates is considered an alternative revenue program of a rate-regulated utility given it permits our Regulated Operating Subsidiaries to adjust future rates in response to past activities or completed events in order to collect our actual revenue requirements under our Formula Rates. In accordance with our accounting policy, only the current year origination of the true-up is reported as a formula rate true-up. Line of Credit Facility [Table] Line of Credit Facility [Table] Retained Earnings [Member] Retained Earnings [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Due from Affiliate, Current Due from Affiliate, Current Schedule of Interest Rate Derivatives [Table Text Block] Schedule of Interest Rate Derivatives [Table Text Block] Additions to property, plant and equipment and other long-lived assets Capital Expenditures Incurred but Not yet Paid Document Period End Date Document Period End Date Statement [Table] Statement [Table] Entity Registrant Name Entity Registrant Name Supplementary Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Dividends to ITC Investment Holdings Inc. Payments of Dividends Payments of Dividends Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Axis] Goodwill and Intangible Assets Disclosure Goodwill and Intangible Assets Disclosure [Text Block] Assets and Liabilities at Fair Value Subject to Three-Tier Hierarchy Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] CASH FLOWS FROM INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Maximum [Member] Maximum [Member] ACCOUNTS RECEIVABLE Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Service cost Defined Benefit Plan, Service Cost Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year Receivables [Abstract] Receivables [Abstract] Unbilled accounts receivable Unbilled Receivables, Current Presiding Administrative Law Judge Initial Decision Presiding Administrative Law Judge Initial Decision [Member] Presiding Administrative Law Judge Initial Decision [Member] Term Loan Credit Agreement, Due January 23, 2021 [Member] Term Loan Credit Agreement, Due January 23, 2021 [Member] Term Loan Credit Agreement, Due January 23, 2021 [Member] Granted Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted Components of accounts receivable Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Retained earnings Retained Earnings (Accumulated Deficit) Entity Tax Identification Number Entity Tax Identification Number Revenue Recognition, Policy Revenue [Policy Text Block] Principal amount Debt Instrument, Face Amount Assets, Excluding Property, Plant, and Equipment, Noncurrent Assets, Excluding Property, Plant, and Equipment, Noncurrent Assets, Excluding Property, Plant, and Equipment, Noncurrent Net Defined Benefit Cost Components Schedule of Net Benefit Costs [Table Text Block] Basis Point Incentive Adder for RTO Participation Basis Point Incentive Adder for RTO Participation Basis Point Incentive Adder for RTO Participation Intercompany payables (less than $1 million) Accounts Payable, Related Parties, Current Minimum [Member] Minimum [Member] Entity Information [Line Items] Entity Information [Line Items] Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Expected amortization expense, year two Finite-Lived Intangible Assets, Amortization Expense, Year Two Regulatory Asset [Domain] Regulatory Asset [Domain] Legal Entity [Axis] Legal Entity [Axis] Deferred income tax expense Deferred Income Tax Expense (Benefit) Statistical Measurement [Domain] Statistical Measurement [Domain] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Entity [Domain] Entity [Domain] INCOME TAX PROVISION Income Tax Expense (Benefit) SHARE-BASED COMPENSATION AND EMPLOYEE SHARE PURCHASE PLAN Share-based Payment Arrangement [Text Block] Contributions in aid of construction Proceeds from Contribution in Aid of Construction Employee Share Purchase Plan Employee Share Purchase Plan [Member] Employee Share Purchase Plan [Member] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Other liabilities Other Liabilities, Noncurrent City Area Code City Area Code Term Loan Credit Agreement, Due June 11, 2021 [Domain] Term Loan Credit Agreement, Due June 11, 2021 [Member] [Member] Term Loan Credit Agreement, Due June 11, 2021 [Member] Operation and maintenance Utilities Operating Expense, Maintenance and Operations Intangible assets (net of accumulated amortization of $44 and $42, respectively) Intangible Assets, Net (Excluding Goodwill) Senior Note, Due May 14, 2030 [Member] Senior Note, Due May 14, 2030 [Member] Senior Note, Due May 14, 2030 MISO Operating Subsidiaries MISO Operating Subsidiaries [Member] MISO Operating Subsidiaries [Member] Other Payments for (Proceeds from) Other Investing Activities Revised Rate Of Return On Equity Revised Rate Of Return On Equity Revised Rate Of Return On Equity Total - assets Assets, Fair Value Disclosure Document - Document and Entity Information [Abstract] Document - Document and Entity Information [Abstract] Document - Document and Entity Information [Abstract] Future Development Payments, Reasonably Possible Estimate Future Development Payments, Reasonably Possible Estimate Future Development Payments, Reasonably Possible Estimate Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Other Other Noncash Income (Expense) Other Comprehensive Loss, reclassification adjustment from AOCI to earnings, Tax of less than $1 million Other Comprehensive Income (Loss), Tax Percent of Dividends Payable Employee Stock Ownership Plan (ESOP), Percent of Dividends Payable Dividends payable by Fortis on the Fortis shares allocated to an employee's ESPP account. Accrued compensation Increase (Decrease) in Employee Related Liabilities Long-term Debt, Gross Long-term Debt, Gross ASSETS TOTAL ASSETS: Assets [Abstract] Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Senior Notes due January 15, 2020 [Member] Senior Notes due January 15, 2020 [Member] Senior Notes due January 15, 2020 [Member] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Expected amortization expense, year three Finite-Lived Intangible Assets, Amortization Expense, Year Three Rate Of Return On Equity Rate Of Return On Equity Rate Of Return On Equity CASH FLOWS FROM OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] Total operating expenses Total operating expenses Operating Expenses Performance Share Units (PSUs) Performance Shares [Member] OTHER EXPENSES (INCOME) Nonoperating Income (Expense) [Abstract] Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Schedule of Financial Information by Reportable Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Segment Reporting [Abstract] Segment Reporting [Abstract] Intangible assets Finite-Lived Intangible Assets, Net Depreciation and amortization expense Depreciation, Depletion and Amortization, Nonproduction Recognition, refund and collection of revenue accruals and deferrals — including accrued interest Increase (Decrease) in Regulatory Assets and Liabilities Debt Disclosure [Abstract] Debt Disclosure [Abstract] Derivative Instrument [Axis] Derivative Instrument [Axis] Supplemental Cash Flow Information [Abstract] Supplemental Cash Flow Information [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] Rate of Return on Equity and Capital Structure Second Complaint Rate of Return on Equity and Capital Structure Second Complaint [Member] Rate of Return on Equity and Capital Structure Second Complaint [Member] Other Comprehensive Loss, reclassification adjustment from AOCI to earnings, pretax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax Impact from Recognition of Liability Impact from Recognition of Liability [Member] Impact from Recognition of Liability [Member] Schedule of Regulatory Assets and Liabilities [Line Items] Schedule of Regulatory Assets and Liabilities [Line Items] [Line Items] for Schedule of Regulatory Assets and Liabilities [Table] ITCTransmission [Member] ITCTransmission [Member] ITCTransmission Fair Value, Assets, Level 2 to Level 1 Transfers, Amount Fair Value, Assets, Level 2 to Level 1 Transfers, Amount Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Fair Value, Net Asset (Liability) Fair Value, Net Asset (Liability) Increase (Decrease) in Accounts Payable Increase (Decrease) in Accounts Payable Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Derivative, Notional Amount Derivative, Notional Amount Required customer refund paid Required customer refund paid Required customer refund paid DEBT Debt Disclosure [Text Block] Derivative, Fixed Interest Rate Derivative, Fixed Interest Rate Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Text Block] Entities [Table] Entities [Table] Common stock, shares authorized Common Stock, Shares Authorized Intangible assets, accumulated amortization Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Entity Central Index Key Entity Central Index Key Entity Emerging Growth Company Entity Emerging Growth Company ITC Midwest LLC [Member] ITC Midwest LLC [Member] ITC Midwest LLC Borrowings under revolving credit agreements Proceeds from Lines of Credit Other current and non-current assets and liabilities, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Long-term debt Long-term Debt, Excluding Current Maturities Equity in capital structure for ratemaking purposes Equity in capital structure for ratemaking purposes Equity in capital structure for ratemaking purposes Accrued compensation Employee-related Liabilities, Current Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 2 [Member] RECENT ACCOUNTING PRONOUNCEMENTS New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Commitment Fee Rate Line of Credit Facility, Commitment Fee Percentage Revenue Accruals, Including Accrued Interest Revenue Accruals, Including Accrued Interest [Member] Revenue Accruals, Including Accrued Interest [Member] LIABILITIES AND STOCKHOLDER’S EQUITY Liabilities and Equity [Abstract] Derivative, Average Variable Interest Rate Derivative, Average Variable Interest Rate Other assets Other Assets, Noncurrent Net refund of 2018 revenue deferrals and accruals, including accrued interest Net Refunds (Collections) Of Revenue Deferrals And Accruals Including Interest Net Refunds (Collections) Of Revenue Deferrals and Accruals, Including Interest, During the Period Book value of revolving credit and term loan credit agreements Line of Credit Facilities and Other Debt, Total Amount Outstanding Line of Credit Facilities and Other Debt, Total Amount Outstanding CASH FLOWS FROM FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Total other comprehensive income, net of tax Derivative instruments, net of tax (Note 11) Total other comprehensive (loss) income, net of tax Other Comprehensive Income (Loss), Net of Tax Type of Adoption [Domain] Type of Adoption [Domain] Derivative Contract [Domain] Derivative Contract [Domain] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Book value of long-term debt and debt maturing within one year, net of discount and deferred financing fees and excluding revolving and term loan credit agreements and commercial paper Long-term Debt NET INCOME: Segment Reporting Information, Operating Income (Loss) [Abstract] Aggregate fair value of PBUs or SBUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount Expected amortization expense, year four Finite-Lived Intangible Assets, Amortization Expense, Year Four Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Expenditures for property, plant and equipment Payments to Acquire Property, Plant, and Equipment Issuance of long-term debt Proceeds from Issuance of Long-term Debt Accrued interest Interest Payable, Current Retirement Plan Type [Domain] Retirement Plan Type [Domain] Employer Match Contribution Employee Stock Ownership Plan (ESOP), Employer Match Contribution ESPP percentage of employer contribution on employee's contribution Regulatory liabilities Non-current regulatory liabilities Regulatory Liability, Noncurrent Network Transmission Load Network Transmission Load Network Transmission Load Other current liabilities Other Liabilities, Current Mutual fund - equity securities [Member] Mutual fund - equity securities [Member] Mutual fund - equity securities [Member] REVENUE Revenue from Contract with Customer [Text Block] Receivable [Domain] Receivable [Domain] Recommended rate of return on equity Recommended Rate of Return on Equity Recommended Rate of Return on Equity Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Interest Rate Debt Instrument, Interest Rate, Stated Percentage Entity Address, Address Line One Entity Address, Address Line One Entity Address, State or Province Entity Address, State or Province Regulated Operating Subsidiaries Operating Segments [Member] Retirement Benefits [Abstract] Retirement Benefits [Abstract] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Fair Value, Assets and Liabilities Measured on Recurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Interest Income, Other Interest Income, Other Incentive Adder for Independent Transmission Ownership Combined Incentive Adders Combined Incentive Adders Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] General and administrative General and Administrative Expense Accrued pension and postretirement liabilities Liability, Defined Benefit Plan, Noncurrent Accounts payable Accounts Payable, Current ITC Holdings Corp. [Member] ITC Holdings Corp. [Member] ITC Holdings Corp. [Member] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Estimated Refund Related to Return on Equity Complaint Estimated Refund Related to Return on Equity Complaint Estimated Refund Related to Return on Equity Complaint Taxes other than income taxes Taxes, Miscellaneous Proceeds from (Repayments of) Other Debt Proceeds from (Repayments of) Other Debt Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party Common stock, without par value Common Stock, No Par Value Entity Interactive Data Current Entity Interactive Data Current Common stock, shares issued Common Stock, Shares, Issued Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Inventory Inventory, Net Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Schedule of Revolving Credit Agreements Schedule of Line of Credit Facilities [Table Text Block] Pension plans Pension Plan [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Property, plant and equipment, accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Award Type [Domain] Award Type [Domain] ITC Great Plains LLC [Member] ITC Great Plains LLC [Member] ITC Great Plains LLC COMMITMENTS AND CONTINGENT LIABILITIES Commitments and Contingencies Disclosure [Text Block] Revolving Credit Facility [Member] Revolving Credit Facility [Member] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Consolidated Entities [Axis] Consolidated Entities [Axis] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Fair value of long-term debt and debt maturing within one year, excluding revolving and term loan credit agreements and commercial paper Long-term Debt, Fair Value Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Allowance for equity funds used during construction Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Allowance for equity funds used during construction Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Liabilities Liabilities Extinguishment of Debt, Amount Extinguishment of Debt, Amount Restatement [Axis] Restatement [Axis] Common stock, without par value, 235,000,000 shares authorized, 224,203,112 shares issued and outstanding at June 30, 2020 and December 31, 2019 Common Stock, Value, Issued Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Net regulatory assets as of December 31, 2019 Net regulatory assets Net regulatory assets Net Regulatory Asset (Liability) Associated with Revenue Accruals and Deferrals Net Regulatory Asset (Liability) Associated with Revenue Accruals and Deferrals Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Related Party Transaction, Other Revenues from Transactions with Related Party (less than $1 million) Related Party Transaction, Other Revenues from Transactions with Related Party Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Equity Components [Axis] Equity Components [Axis] New Accounting Pronouncements or Change in Accounting Principle New Accounting Pronouncements or Change in Accounting Principle [Line Items] Employee Benefits and Share-based Compensation Employee Benefits and Share-based Compensation Total stockholder’s equity Stockholders' Equity Attributable to Parent Stockholders' Equity Attributable to Parent Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Amortization expense Amortization of Intangible Assets Supplemental Cash Flow Elements [Abstract] Supplemental Cash Flow Elements [Abstract] Refundable deposits and advances for construction Contract with Customer, Liability, Current Regulated Operations [Abstract] Regulated Operations [Abstract] FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] METC LLC [Member] METC LLC [Member] METC LLC [Member] Regulatory Liabilities [Line Items] Regulatory Liabilities [Line Items] Other Comprehensive Income (Loss), Gain (Loss) on Derivatives Qualifying as Hedges, Tax Other Comprehensive Income (Loss), Gain (Loss) on Derivatives Qualifying as Hedges, Tax Other Comprehensive Income (Loss), Gain (Loss) on Derivatives Qualifying as Hedges, Tax Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] REGULATORY MATTERS Public Utilities Disclosure [Text Block] Interest paid (net of interest capitalized) Interest Paid, Excluding Capitalized Interest, Operating Activities Forecast [Member] Forecast [Member] Revenue Accruals and Deferrals Revenue Accruals and Deferrals [Abstract] Revenue Accruals and Deferrals [Abstract] Cash equivalents Cash and Cash Equivalents, Fair Value Disclosure Other Postretirement Benefits Plan Other Postretirement Benefits Plan [Member] Depreciation and amortization Utilities Operating Expense, Depreciation and Amortization Regulatory assets Non-current regulatory assets Regulatory Assets, Noncurrent Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Equity Component [Domain] Equity Component [Domain] Document Transition Report Document Transition Report Intercompany tax payable to subsidiaries Intercompany tax payable to subsidiaries Intercompany tax payable to subsidiaries Accrued taxes Taxes Payable, Current Intercompany receivables (less than $1 million) Accounts Receivable, Related Parties, Current Regulatory assets Current regulatory assets Regulatory Assets, Current Consolidated Entities [Domain] Consolidated Entities [Domain] Net Changes in Regulatory Assets and Liabilities Schedule Of Changes In Regulatory Assets And Liabilities Formula Rate Revenue Accruals And Deferrals Table Text Block The changes in regulatory assets and liabilities (net) associated with our Regulated Operating Subsidiaries' formula rate revenue accruals and deferrals, including accrued interest, from the beginning of the period through the current reporting period. Other Pension Plan [Member] Other Pension Plan [Member] Commercial Paper Program, Maximum Authorized Amount Outstanding Commercial Paper Program, Maximum Authorized Amount Outstanding Commercial Paper Program, Maximum Authorized Amount Outstanding Income Statement [Abstract] Income Statement [Abstract] Revenue true-up amount reflected in customer bill, period of recognition Revenue True-up Amount Reflected In Customer Bill, Period of Recognition The time period from the time the true-up amount is calculated from revenue accruals and deferrals based on revenue requirements to the time the true-up amount is reflected in customer bills. Customer Refund Liability, Current Refunded to Customers Refunded to Customers Employee Stock Ownership Plan (ESOP) Name [Axis] Employee Stock Ownership Plan (ESOP) Name [Axis] Fair Value, Assets, Level 1 to Level 2 Transfers, Amount Fair Value, Assets, Level 1 to Level 2 Transfers, Amount