Goodwill and Intangible Assets Disclosure [Abstract] GOODWILL AND INTANGIBLE ASSETS Goodwill and Intangible Assets Disclosure [Text Block] Regulated Operations [Abstract] REGULATORY MATTERS Public Utilities Disclosure [Text Block] Compensation and Retirement Disclosure [Abstract] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefits Plans Disclosures [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefits Plans [Domain] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Defined Benefit Plans Pension Plan [Member] Other Postretirement Benefits Plan Other Postretirement Benefit Plan [Member] Defined Benefit Plan Disclosure Defined Benefit Plan Disclosure [Line Items] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return on Plan Assets Net cost Defined Benefit Plan, Net Periodic Benefit Cost Organization, Consolidation and Presentation of Financial Statements [Abstract] GENERAL Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Disclosure of Compensation Related Costs, Share-based Payments [Abstract] SHARE-BASED COMPENSATION Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Regulated operations Operating Segments [Member] ITC Holdings and other Corporate, Non-Segment [Member] Intercompany eliminations Intersegment Eliminations [Member] Segment Reporting Information Segment Reporting Information [Line Items] OPERATING REVENUES: Segment Reporting Information, Revenue for Reportable Segment [Abstract] Operating revenues Electric Revenue INCOME (LOSS) BEFORE INCOME TAXES: Segment Reporting Information, Income (Loss) before Income Taxes [Abstract] Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest NET INCOME: Segment Reporting Information, Operating Income (Loss) [Abstract] NET INCOME Net Income (Loss) Attributable to Parent TOTAL ASSETS: Assets [Abstract] Assets Assets Statement of Comprehensive Income [Abstract] Statement [Table] Statement [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Statement [Line Items] Statement [Line Items] OTHER COMPREHENSIVE LOSS Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Derivative instruments, net of tax (Note 7) Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax TOTAL COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Attributable to Parent New Accounting Pronouncements and Changes in Accounting Principles [Abstract] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-09 Accounting Standards Update 2016-09 [Member] Accounting Standards Update 2016-09 [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Reported Scenario, Previously Reported [Member] Adjustment Restatement Adjustment [Member] New Accounting Pronouncements or Change in Accounting Principle New Accounting Pronouncements or Change in Accounting Principle [Line Items] INCOME TAX PROVISION Income Tax Expense (Benefit) Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] GIC Private Limited GIC Private Limited [Member] GIC Private Limited [Member] ITC Holdings Parent Company [Member] Type Of Operating Cost And Expense [Axis] Type Of Operating Cost And Expense [Axis] Type Of Operating Cost And Expense [Axis] Type Of Operating Cost And Expense [Domain] Type Of Operating Cost And Expense [Domain] Type Of Operating Cost And Expense Certain Internal Labor and Associated Costs Certain Internal Labor and Associated Costs [Member] Certain Internal Labor and Associated Costs [Member] External Legal, Advisory and Financial Services Fees External Legal, Advisory and Financial Services Fees [Member] External Legal, Advisory and Financial Services Fees [Member] The Merger Business Acquisition [Line Items] Ownership percentage of minority investor upon completion of merger Ownership Percentage of Minority Investor Upon Completion of Merger Ownership Percentage of Minority Investor Upon Completion of Merger Business acquisition, cash consideration Business Combination, Consideration, Cash Paid by Minority Investor Business Combination, Consideration, Cash Paid Minority Investor Cash per common share Business Combination, Consideration, Cash Per Common Share Business Combination, Consideration, Cash Per Common Share Fortis stock per common share Business Combination, Consideration, Stock Per Common Share Business Combination, Consideration, Stock Per Common Share Ownership percentage of Fortis after close of merger Ownership Percentage of Acquirer Upon Completion of Merger Ownership Percentage of Acquirer Upon Completion of Merger Merger consideration share-based compensation awards Merger consideration share-based compensation awards Merger consideration share-based compensation awards Merger related expenses Business Combination, Acquisition Related Costs Equity [Abstract] Balance at the beginning of period Accumulated Other Comprehensive Income (Loss), Net of Tax Loss on interest rate swaps relating to interest rate cash flow hedges (net of tax of $2 for the three months ended March 31, 2016) (a) Other Comprehensive Income (Loss), Gain (Loss) on Derivatives Qualifying as Hedges, Net of Tax Amount after tax of increase (decrease) in accumulated gain (loss) upon settlement of derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss). Unrealized gains on available-for-sale securities, net of tax Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Reclassification of net loss relating to interest rate cash flow hedges from AOCI to interest expense, net of tax Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Balance at the end of period (b) (c) Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Expectation Scenario, Forecast [Member] Portion expected to be reclassified from AOCI to interest expense during the next twelve months Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax Cash Dividends Paid to Parent Company by Consolidated Subsidiaries Cash Dividends Paid to Parent Company by Consolidated Subsidiaries Schedule of Financial Information by Reportable Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Income Statement [Abstract] OPERATING REVENUES OPERATING EXPENSES Costs and Expenses [Abstract] Operation and maintenance Utilities Operating Expense, Maintenance and Operations General and administrative General and Administrative Expense Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Taxes other than income taxes Taxes, Other Total operating expenses Costs and Expenses OPERATING INCOME Operating Income (Loss) OTHER EXPENSES (INCOME) Nonoperating Income (Expense) [Abstract] Interest expense — net Interest Expense Allowance for equity funds used during construction Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Other expense Other Nonoperating Expense Total other expenses (income) Nonoperating Income (Expense) INCOME BEFORE INCOME TAXES NET INCOME Schedule of Regulatory Matters Public Utilities General Disclosures [Table] Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Regional Cost Allocation Refund Regional Cost Allocation Refund [Member] Regional Cost Allocation Refund [Member] Schedule of Regulatory Matters Public Utilities, General Disclosures [Line Items] Current regulatory assets Regulatory Assets, Current Transmission rate, applicable period Transmission Rate, Applicable Period Transmission Rate, Applicable Period 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. Supplementary Cash Flows Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Supplementary cash flows information: Supplemental Cash Flow Information [Abstract] Interest paid (net of interest capitalized) (a) Interest Paid, Net Income taxes paid Income Taxes Paid Interest paid associated with the ROE complaints Interest paid associated with the ROE complaints Interest paid associated with the ROE complaints Supplementary non-cash investing and financing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Additions to property, plant and equipment and other long-lived assets Capital Expenditures Incurred but Not yet Paid Allowance for equity funds used during construction Debt Disclosure [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] ITCTransmission ITCTransmission [Member] ITCTransmission METC METC LLC [Member] METC LLC [Member] ITC Midwest ITC Midwest LLC [Member] ITC Midwest LLC ITC Great Plains ITC Great Plains LLC [Member] ITC Great Plains LLC Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Total available capacity Line of Credit Facility, Current Borrowing Capacity Outstanding balance Long-term Line of Credit Unused capacity Line of Credit Facility, Remaining Borrowing Capacity Weighted average interest rate Debt, Weighted Average Interest Rate Commitment fee rate Line of Credit Facility, Commitment Fee Percentage Unused capacity, adjusted for commercial paper outstanding Line of Credit Facility, Remaining Borrowing Capacity Adjusted for Commercial Paper Outstanding Line of Credit Facility, Remaining Borrowing Capacity Adjusted for Commercial Paper Outstanding Interest rate description Line of Credit Facility, Interest Rate Description Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Schedule of Regulatory Assets and Liabilities [Table] Regulatory Asset [Axis] Regulatory Asset [Axis] Regulatory Asset [Domain] Regulatory Asset [Domain] Revenue Accruals, Including Accrued Interest Revenue Accruals, Including Accrued Interest [Member] Revenue Accruals, Including Accrued Interest [Member] Regulatory Liability [Axis] Regulatory Liability [Axis] Regulatory Liability [Domain] Regulatory Liability [Domain] Revenue Deferrals, Including Accrued Interest Revenue Deferrals, Including Accrued Interest [Member] Revenue Deferrals, Including Accrued Interest [Member] Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Line Items] [Line Items] for Schedule of Regulatory Assets and Liabilities [Table] Non-current regulatory assets Regulatory Assets, Noncurrent Current regulatory liabilities Regulatory Liability, Current Non-current regulatory liabilities Regulatory Liability, Noncurrent Ending balance Net Regulatory Asset (Liability) Associated with Revenue Accruals and Deferrals Net Regulatory Asset (Liability) Associated with Revenue Accruals and Deferrals Commitments and Contingencies Disclosure [Abstract] Commitments and Contingent Liabilities [Table] Commitments and Contingent Liabilities [Table] Commitments and Contingent Liabilities [Table] Public Utilities, Regulatory Complaint [Axis] Public Utilities, Regulatory Complaint [Axis] Public Utilities, Regulatory Complaint [Axis] Public Utilities, Regulatory Complaint [Domain] Public Utilities, Regulatory Complaint [Domain] [Domain] for Public Utilities, Regulatory Complaint [Axis] 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] ITCTransmission MISO Operating Subsidiaries MISO Operating Subsidiaries [Member] MISO Operating Subsidiaries [Member] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Sales and Use Tax Audit Sales and Use Tax Audit [Member] Sales and Use Tax Audit [Member] Rate of Return on Equity and Capital Structure Initial Complaint 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 True-up Rate of Return on Equity and Capital Structure Initial Complaint True-up [Member] Rate of Return on Equity and Capital Structure Initial Complaint True-up [Member] 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] Public Utilities Regulatory Complaint Proceeding Items [Axis] Public Utilities Regulatory Complaint Proceeding Items [Axis] Public Utilities Regulatory Complaint Proceeding Items [Axis] Public Utilities Regulatory Complaint Proceeding Items [Domain] Public Utilities Regulatory Complaint Proceeding Items [Domain] [Domain] for Public Utilities Regulatory Complaint Proceeding Items [Axis] Expert Witness Testimony Expert Witness Testimony [Member] Expert Witness Testimony [Member] FERC Order FERC Order [Member] FERC Order [Member] Presiding Administrative Law Judge Initial Decision Presiding Administrative Law Judge Initial Decision [Member] Presiding Administrative Law Judge Initial Decision [Member] Estimated Potential Refund Related to Return on Equity Complaints Estimated Potential Refund Related to Return on Equity Complaints [Member] Estimated Potential Refund Related to Return on Equity Complaints [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Impact from Recognition of Liability [Axis] Impact from Recognition of Liability [Axis] Impact from Recognition of Liability [Axis] Impact from Recognition of Liability [Domain] Impact from Recognition of Liability [Domain] [Domain] for Impact from Recognition of Liability [Axis] Impact from Recognition of Liability Impact from Recognition of Liability [Member] Impact from Recognition of Liability [Member] Commitments and Contingent Liabilities Commitments and Contingent Liabilities [Line Items] Commitments and Contingent Liabilities [Line Items] Potential liability Tax, Estimate of Potential Liability Tax, Estimate of Potential Liability Rate of return on equity Rate Of Return On Equity Rate Of Return On Equity Reduced rate of return on equity Reduced Rate of Return on Equity Reduced Rate of Return on Equity FERC approved capital structure, equity percentage FERC Approved Capital Structure, Equity Percentage FERC Approved Capital Structure, Equity Percentage Complaint capital structure, equity percentage Complaint Capital Structure, Equity Percentage Complaint Capital Structure, Equity Percentage Revised rate of return on equity Revised Rate Of Return On Equity Revised Rate Of Return On Equity Current regulatory liability Payments for Other Operating Activities Payments for Other Operating Activities Regulatory assets Recommended rate of return on equity Recommended Rate of Return on Equity Recommended Rate of Return on Equity Estimated potential refund Loss Contingency, Estimate of Possible Loss Non-current regulatory liability Interest expense Equity in capital structure for ratemaking purposes Equity in capital structure for ratemaking purposes Equity in capital structure for ratemaking purposes 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 Approved incentive adder for RTO participation Approved Return on Equity Rate Incentive Adder for Participation in Regional Transmission Organization Approved Return on Equity Rate Incentive Adder for Participation in Regional Transmission Organization Requested incentive adder for RTO participation Requested Return on Equity Rate Incentive Adder for Participation in Regional Transmission Organization Requested Return on Equity Rate Incentive Adder for Participation in Regional Transmission Organization Requested incentive adder for independence Requested Return on Equity Rate Incentive Adder for Independent Transmission Ownership Requested Return on Equity Rate Incentive Adder for Independent Transmission Ownership Approved incentive adder for independence Approved Return on Equity Rate Incentive Adder for Independent Transmission Ownership Approved Return on Equity Rate Incentive Adder for Independent Transmission Ownership Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Fair Value Disclosures [Abstract] 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] SEGMENT INFORMATION Segment Reporting Disclosure [Text Block] Schedule of Retirement Benefits Disclosures [Table] Schedule of Retirement Benefits Disclosures [Table] Schedule of Retirement Benefits Disclosures [Table] Other Pension Plan Other Pension Plan [Member] Supplemental Retirement Plans Supplemental Employee Retirement Plan [Member] Defined Contribution Plan Type [Axis] Defined Contribution Plan Type [Axis] Defined Contribution Plan Type [Domain] Defined Contribution Plan Type [Domain] Defined Contribution Plan Defined Contribution Retirement Savings Plan [Member] Defined Contribution Retirement Savings Plan [Member] Expectation Retirement Benefits Disclosure Retirement Benefits Disclosure [Line Items] Retirement Benefits Disclosure [Line Items] Expected additional current year contribution Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year Plan cost Defined Contribution Plan, Cost Recognized Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Expense Recognized Upon Completion of the Merger Expense Recognized Upon Completion of the Merger [Member] Expense Recognized Upon Completion of the Merger [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] 2017 Omnibus Plan 2017 Omnibus Plan [Member] 2017 Omnibus Plan [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Performance Shares Performance Shares [Member] Service-Based Units Service-Based Units [Member] Service-Based Units [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Shares issued in period Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period 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 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 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 Statement of Financial Position [Abstract] ASSETS Current assets Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Accounts receivable Accounts Receivable, Net, Current Inventory Inventory, Net Income tax receivable Income Taxes Receivable, Current Prepaid and other current assets Prepaid Expense and Other Assets, Current Total current assets Assets, Current Property, plant and equipment (net of accumulated depreciation and amortization of $1,608 and $1,575, respectively) Property, Plant and Equipment, Net Other assets Other Assets [Abstract] Goodwill Goodwill Intangible assets (net of accumulated amortization of $33 and $32, respectively) Finite-Lived Intangible Assets, Net Regulatory assets Deferred financing fees (net of accumulated amortization of $2 and $2, respectively) Debt Issuance Costs, Noncurrent, Net Other Other Assets, Noncurrent Total other assets Assets, Noncurrent TOTAL ASSETS LIABILITIES AND STOCKHOLDER’S EQUITY Liabilities and Equity [Abstract] Current liabilities Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued compensation Employee-related Liabilities, Current Accrued interest Interest Payable, Current Accrued taxes Taxes Payable, Current Regulatory liabilities Refundable deposits from generators for transmission network upgrades Refundable Deposits From Generators For Transmission Network Upgrades, Current For utilities only, represents the current portion (expected to be paid within 1 year) of the carrying amount of the liability as of the balance sheet date for payments received by a utility from its customers in advance of performing its obligations under terms of its construction agreements. Debt maturing within one year Long-term Debt, Current Maturities Other Other Liabilities, Current Total current liabilities Liabilities, Current Accrued pension and postretirement liabilities Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Deferred income taxes Deferred Tax Liabilities, Net, Noncurrent Regulatory liabilities Refundable deposits from generators for transmission network upgrades Customer Advances for Construction Other Other Liabilities, Noncurrent Long-term debt Long-term Debt, Excluding Current Maturities Commitments and contingent liabilities (Notes 4 and 11) Commitments and Contingencies STOCKHOLDER’S EQUITY Stockholders' Equity Attributable to Parent [Abstract] Common stock, without par value, 235,000,000 shares authorized, 224,203,112 shares issued and outstanding at March 31, 2017 and December 31, 2016 Common Stock, Value, Issued Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income Total stockholder’s equity Stockholders' Equity Attributable to Parent TOTAL LIABILITIES AND STOCKHOLDER’S EQUITY Liabilities and Equity RECENT ACCOUNTING PRONOUNCEMENTS New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Schedule of Outstanding Interest Rate Swaps Schedule of Interest Rate Derivatives [Table Text Block] Schedule of Revolving Credit Agreements Schedule of Line of Credit Facilities [Table Text Block] Changes in Accumulated Other Comprehensive Income Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] STOCKHOLDER'S EQUITY Stockholders' Equity Note Disclosure [Text Block] THE MERGER Mergers, Acquisitions and Dispositions Disclosures [Text Block] Statement of Cash Flows [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] 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] Depreciation and amortization expense Recognition, refund and collection of revenue accruals and deferrals — including accrued interest Increase (Decrease) in Regulatory Assets and Liabilities Deferred income tax expense Deferred Income Tax Expense (Benefit) Other Other Noncash Income (Expense) Changes in assets and liabilities, exclusive of changes shown separately: Increase (Decrease) in Operating Capital [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Income tax receivable Increase (Decrease) in Income Taxes Receivable Other current assets Increase (Decrease) in Prepaid Expense and Other Assets Accounts payable Increase (Decrease) in Accounts Payable Accrued compensation Increase (Decrease) in Employee Related Liabilities Accrued interest Increase (Decrease) in Interest Payable, Net Accrued taxes Increase (Decrease) in Accrued Taxes Payable Other current liabilities Increase (Decrease) in Other Current Liabilities Net estimated refund related to return on equity complaints Increase (Decrease) in Estimated Potential Refund Related to Return on Equity Complaints The increase (decrease) during the reporting period in the estimated potential refund related to return on equity complaints. Other non-current assets and liabilities, net Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Expenditures for property, plant and equipment Payments to Acquire Property, Plant, and Equipment Contributions in aid of construction Proceeds from Contribution in Aid of Construction Other Payments for (Proceeds from) Other Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Borrowings under revolving credit agreements Proceeds from Lines of Credit Borrowings under term loan credit agreements Proceeds from Other Debt Net (retirement) issuance of commercial paper, net of discount Proceeds from (Repayments of) Commercial Paper Repayments of revolving credit agreements Repayments of Lines of Credit Dividends on common and restricted stock Payments of Ordinary Dividends, Common Stock Dividends to ITC Investment Holdings Inc. Payments of Dividends Refundable deposits from generators for transmission network upgrades Refundable Deposits from Generators for Transmission Network Upgrades, Financing Activities Change in refundable deposits from generators for transmission network upgrades. Other Proceeds from (Payments for) Other Financing Activities Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities NET DECREASE IN CASH AND CASH EQUIVALENTS Cash and Cash Equivalents, Period Increase (Decrease) CASH AND CASH EQUIVALENTS — Beginning of period CASH AND CASH EQUIVALENTS — End of period Fair Value, Assets and Liabilities Measured on Recurring Basis [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value by Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring Basis Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Asset and Liability Class [Axis] Asset and Liability Class [Axis] Asset and Liability Class [Axis] Asset and Liability Class [Domain] Asset and Liability Class [Domain] [Domain] for Asset and Liability Class [Axis] Fixed Income Securities Fixed Income Securities [Member] Equity Securities Equity Securities [Member] Interest Rate Swap Interest Rate Swap [Member] Fair Value, Assets and Liabilities Measured on Recurring Basis Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair value, level transfers Fair Value, Assets, Level Transfers, Amount Fair Value, Assets, Level Transfers, Amount Mutual funds Investments, Fair Value Disclosure Interest rate swap fair value, asset Derivative Asset, Fair Value, Gross Asset Interest rate swaps fair value, liability Derivative Liability, Fair Value, Gross Liability Total - asset Assets, Fair Value Disclosure Total - net liability Financial and Nonfinancial Liabilities, Fair Value Disclosure Property, plant and equipment, accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Intangible assets, accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Deferred financing fees, accumulated amortization Accumulated Amortization, Debt Issuance Costs, Noncurrent Common stock, par value Common Stock, No 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 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. Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Text Block] Schedule of New Accounting Pronouncements and Changes in Accounting Principles Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Schedule of Goodwill and Intangible Assets [Table] Schedule of Goodwill and Intangible Assets [Table] Schedule of Goodwill and Intangible Assets [Table] Goodwill and Intangible Assets Goodwill and Intangible Assets [Line Items] Goodwill and Intangible Assets [Line Items] Intangible assets Accumulated amortization Amortization expense Amortization of Intangible Assets Expected amortization expense, year one Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months Expected amortization expense, year two Finite-Lived Intangible Assets, Amortization Expense, Year Two Expected amortization expense, year three Finite-Lived Intangible Assets, Amortization Expense, Year Three Expected amortization expense, year four Finite-Lived Intangible Assets, Amortization Expense, Year Four Expected amortization expense, year five Finite-Lived Intangible Assets, Amortization Expense, Year Five RETIREMENT BENEFITS AND ASSETS HELD IN TRUST Pension and Other Postretirement Benefits Disclosure [Text Block] Revenue Accruals and Deferrals Revenue Accruals and Deferrals [Abstract] Revenue Accruals and Deferrals [Abstract] Beginning balance Net collection of 2015 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 Net revenue accrual for the three months ended March 31, 2017 Net Revenue Accruals (Deferrals) For The Period Net Revenue Accruals (Deferrals) For The Period FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] COMMITMENTS AND CONTINGENT LIABILITIES Commitments and Contingencies Disclosure [Text Block] Derivative [Table] Derivative [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Senior Notes, due January 31, 2018 Senior Notes due January 31, 2018 [Member] Senior Notes due January 31, 2018 [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Derivative Derivative [Line Items] Long-term debt Notional amount Derivative, Notional Amount Fixed rate Derivative, Fixed Interest Rate Term of contract Derivative, Term of Contract Interest rate swap fair value, asset Interest rate swaps fair value, liability DEBT Debt Disclosure [Text Block] Document - Document and Entity Information [Abstract] Document - Document and Entity Information [Abstract] Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Trading Symbol Trading Symbol Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Schedule of Net Defined Benefit Cost Components Schedule of Net Benefit Costs [Table Text Block] Schedule of Debt Instruments [Table] Schedule of Debt Instruments [Table] Schedule of Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Unsecured Debt Unsecured Debt [Member] Secured Debt Secured Debt [Member] Term Loan Credit Agreement, Due March 24, 2018 [Member] Term Loan Credit Agreement, Due March 24, 2018 [Member] Term Loan Credit Agreement, Due March 24, 2018 First Mortgage Bonds, Series H, due April 18, 2047 [Member] First Mortgage Bonds, Series H, due April 18, 2047 [Member] First Mortgage Bonds, Series H, due April 18, 2047 [Member] Term Loan Credit Agreement, Due March 23, 2019 [Member] Term Loan Credit Agreement, Due March 23, 2019 [Member] Term Loan Credit Agreement, Due March 23, 2019 [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Commercial paper program, maximum authorized amount outstanding Commercial Paper Program, Maximum Authorized Amount Outstanding Commercial Paper Program, Maximum Authorized Amount Outstanding Commercial paper Commercial Paper Commercial paper, weighted average interest rate Short-term Debt, Weighted Average Interest Rate Commercial paper, weighted average days to maturity Short-Term Debt, Weighted Average Days to Maturity Short-Term Debt, Weighted Average Days to Maturity Term loan Other Long-term Debt Principal amount Debt Instrument, Face Amount Interest rate Debt Instrument, Interest Rate, Stated Percentage