Guarantor Obligations [Line Items] Guarantor Obligations [Line Items] Statistical Measurement [Domain] Statistical Measurement [Domain] Entity Listings, Exchange [Axis] Entity Listings, Exchange [Axis] Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Award Timing Predetermined Award Timing Predetermined [Flag] Entity File Number Entity File Number Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Share of affiliates' earnings, net of taxes Income (Loss) from Equity Method Investments Tabular List, Table Tabular List [Table Text Block] Leases [Abstract] Leases [Abstract] Debt Debt and Lease Obligation [Abstract] Pledged Status [Axis] Pledged Status [Axis] Carrying amounts and fair values of other financial instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Interest (expense) income, net Interest Income (Expense), Nonoperating Total commercial commitments Guarantor Obligations, Maximum Exposure, Undiscounted Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Measurement Basis [Axis] Measurement Basis [Axis] Basic earnings per share (in dollars per share) Basic earnings per share from consolidated operations (in dollars per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Revenue Revenue from Contract with Customer [Text Block] Award Date [Axis] Award Date [Axis] Other comprehensive (loss) income Other Comprehensive Income (Loss), Net of Tax Schedule of Segment Data Schedule of Segment Reporting Information, by Segment [Table Text Block] Leases by Type [Domain] Leases by Type [Domain] Leases by Type [Domain] Adjustment to Compensation, Amount Adjustment to Compensation Amount Defined Benefit Pension [Member] Pension Plan [Member] Railcar Acquisition Railcar Acquisition [Member] Railcar Acquisition Employee Stock Option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Schedule of Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Recourse Recourse debt (1) Recourse Debt Recourse debt. Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Dividends, Common Stock, Cash Dividends, Common Stock, Cash Asset impairments Asset Impairment Charges Total Shareholders’ Equity Beginning balance Ending balance Equity, Attributable to Parent Measurement Frequency [Axis] Measurement Frequency [Axis] Insider Trading Policies and Procedures [Line Items] Share-based compensation expense Share-Based Payment Arrangement, Expense Operating Assets and Facilities Property, Plant and Equipment [Table Text Block] Common stock, shares authorized Common Stock, Shares Authorized Hedging Designation [Domain] Hedging Designation [Domain] NYSE Texas, Inc NYSE CHICAGO, INC. [Member] Operating lease revenue: Operating Lease, Lease Income [Abstract] Stock Issued During Period, Shares, New Issues Stock Issued During Period, Shares, New Issues Total Liabilities and Shareholders’ Equity Liabilities and Equity Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Fair Value, Recurring [Member] Fair Value, Recurring [Member] Post-Retirement Benefit Plans Adjustments Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward] Liabilities and Shareholders’ Equity Liabilities and Equity [Abstract] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Property, Plant and Equipment, Net [Abstract] Property, Plant and Equipment, Net [Abstract] Net loss Net loss attributable to non-controlling interest Net Income (Loss) Attributable to Noncontrolling Interest Guarantees [Abstract] Guarantees [Abstract] Asset Acquisition Asset Acquisition [Text Block] Restricted Stock [Member] Restricted Stock [Member] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component Treasury Stock, Common Treasury Stock, Common [Member] Net gains on sales of assets Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Borrowings under bank credit facilities Debt, Long-Term and Short-Term, Combined Amount Operating leases Operating leases Operating Lease, Liability Retirement Benefits [Abstract] Retirement Benefits [Abstract] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Entity Shell Company Entity Shell Company Recourse Status [Domain] Recourse Status [Domain] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Derivative, Amount of Hedged Item Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge Recourse Fixed Rate Debt Fair Value Disclosure Recourse Fixed Rate Debt Fair Value Disclosure Recourse fixed rate debt fair value disclosure. Variable Interest Entity [Table] Variable Interest Entity [Table] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Other comprehensive loss attributable to non-controlling interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Comprehensive Income Attributable to GATX Comprehensive Income (Loss), Net of Tax, Attributable to Parent Name Measure Name Equity, Attributable to Noncontrolling Interest [Roll Forward] Equity, Attributable to Noncontrolling Interest [Roll Forward] Deferred income taxes Deferred Income Tax Liabilities, Net Document Fiscal Period Focus Document Fiscal Period Focus Award Timing Method Award Timing Method [Text Block] Award Type [Axis] Award Type [Axis] Foreign Currency Translation Adjustments Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Hedging Relationship [Domain] Hedging Relationship [Domain] Legal Entity [Axis] Legal Entity [Axis] Total Assets Identifiable assets Assets Finance leases (as lessor) Direct Financing Lease, Net Investment in Lease, before Allowance for Credit Loss Investment, Name [Domain] Investment, Name [Domain] Trading Symbol Trading Symbol Entity Address, City or Town Entity Address, City or Town Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Document And Entity Information. Leases by Type [Axis] Leases by Type [Axis] Operating Leases by Type. 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Interest Expense [Member] Interest Expense [Member] Other Assets Other assets Other Assets Document Information [Line Items] Document Information [Line Items] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Hedging Relationship [Axis] Hedging Relationship [Axis] Operating Assets and Facilities Property, Plant and Equipment, Gross Property, Plant and Equipment, Gross Parent Parent [Member] Net Income Net Income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Derivative, notional amount Derivative, Notional Amount Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Guarantor Obligation [Table] Guarantor Obligation [Table] Other Income (Expense) Other Income and Expenses [Abstract] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Buildings, leasehold improvements, and other equipment Building and Building Improvements [Member] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Other Other Business Segments [Member] Other business segments. Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Fair Value Hedging [Member] Fair Value Hedging [Member] Defined Benefit Plan, Amortization of Gain (Loss) Defined Benefit Plan, Amortization of Gain (Loss) Cash Flow Hedging Cash Flow Hedging [Member] Other Liabilities Other liabilities Other Liabilities Goodwill Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Total depreciation expense Depreciation Equity Components [Axis] Equity Components [Axis] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Portfolio Management Portfolio Management [Member] Portfolio management. Description of Business Nature of Operations [Text Block] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Number of Reportable Segments Number of Reportable Segments Variable Interest Entities Variable Interest Entity Disclosure [Text Block] Other Performance Measure, Amount Other Performance Measure, Amount Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax Entity Address, State or Province Entity Address, State or Province Engine Leasing Engine Leasing [Member] Engine Leasing Effective Income Tax Rate Reconciliation, Amount [Abstract] Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract] Components of Lease Income Direct Financing Lease, Lease Income [Table Text Block] Derivative Instrument [Axis] Derivative Instrument [Axis] Individual: Individual [Axis] Vesting [Axis] Vesting [Axis] Restricted cash Restricted Cash Computation of basic and diluted net income per common share Earnings Per Share Reconciliation [Abstract] Accounting Changes and Error Corrections [Abstract] Accounting Changes and Error Corrections [Abstract] Entity [Domain] Entity [Domain] Net cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Investments in Affiliated Companies Investments in affiliated companies Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Proceeds from Noncontrolling Interests Proceeds from Noncontrolling Interests Document Fiscal Year Focus Document Fiscal Year Focus Right-of-use assets, net of accumulated depreciation Operating Lease, Right-of-Use Asset Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Repayments of debt with original maturities longer than 90 days Cash paid for the repayment of debt Repayments of Long-Term Debt Effective Income Tax Rate Reconciliation, Percent Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Plan Name [Domain] Plan Name [Domain] Reported Value Measurement [Member] Reported Value Measurement [Member] Legal Proceedings and Other Contingencies Legal Matters and Contingencies [Text Block] Financial Data of Business Segments Segment Reporting Disclosure [Text Block] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Not Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument [Member] Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Numerator: Net Income Loss Available to Common Stockholders Basic and Dilutive [Abstract] Net income loss available to common stockholders basic and dilutive. Ownership [Domain] Ownership [Domain] Other Other Capitalized Property Plant and Equipment [Member] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Accumulated Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Rail North America Rail North America [Member] Rail. Selling, general and administrative expense Selling, General and Administrative Expense Exchange [Domain] Exchange [Domain] Accumulated other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Joint venture, ownership interest Joint Venture, Ownership Interest Joint Venture, Ownership Interest Depreciation, Depletion and Amortization Depreciation, Depletion and Amortization Entity Central Index Key Entity Central Index Key PEO Name PEO Name Total Revenues Total revenues Revenues Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Tank containers Tank Containers [Member] Tank Containers Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Defined Benefit Plan [Table] Defined Benefit Plan [Table] Arrangement Duration Trading Arrangement Duration Rail International Rail International [Member] Rail International [Member] Income taxes expense (benefit) including affiliate's earnings Income taxes expense (benefit) including affiliate's earnings Income taxes expense (benefit) including affiliate's earnings Segments [Axis] Segments [Axis] Income taxes, affiliates' earnings Provision for Income Taxes, Equity Method Investment Provision for Income Taxes, Equity Method Investment Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Class of Stock [Domain] Class of Stock [Domain] Portfolio proceeds Portfolio Proceeds Portfolio Proceeds Portfolio proceeds. Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Rent and other receivables Accounts Receivable, before Allowance for Credit Loss, Current Other Payment for (Proceeds from) Other Investing Activity Share-Based Compensation Share-Based Payment Arrangement [Text Block] Residual sharing income Nonoperating Income, Residual Sharing Income Nonoperating Income, Residual Sharing Income Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) Hedged Asset, Fair Value Hedge, Cumulative Increase (Decrease) Assets Assets [Abstract] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Vesting [Domain] Vesting [Domain] Pension and Other Post-Retirement Benefits Retirement Benefits [Text Block] Fair Value Fair Value Disclosures [Text Block] Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Shareholders’ Equity Equity, Attributable to Parent [Abstract] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Address Line One Entity Address, Address Line One AOCI Attributable to Parent [Member] AOCI Attributable to Parent [Member] Investment, Name [Axis] Investment, Name [Axis] Less: allowance for losses Accounts Receivable, Allowance for Credit Loss, Current Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] Ownership [Axis] Ownership [Axis] Railcars and locomotives Railroad Transportation Equipment [Member] Fair Value as of Grant Date Award Grant Date Fair Value Property, Plant and Equipment [Abstract] Entity Registrant Name Entity Registrant Name Gain (loss) on cash flow hedges expected to be reclassified within next twelve months, net of tax Cash Flow Hedge Gain (Loss) to be Reclassified within 12 Months Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table] Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table] Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total Defined Benefit Plan, Net Periodic Benefit Cost (Credit) NEW YORK STOCK EXCHANGE, INC. NEW YORK STOCK EXCHANGE, INC. [Member] Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Equity compensation plans Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Cash flow hedging instruments Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Total expenses (1) Total expenses (1) Costs and Expenses Document Quarterly Report Document Quarterly Report Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Counterparty Name [Domain] Counterparty Name [Domain] Number of business segments Number of Operating Segments Commercial Commitments Guarantees [Text Block] Receivables Loans and Leases Receivable, Net Amount [Abstract] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Interest cost Defined Benefit Plan, Interest Cost Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Restatement Determination Date: Restatement Determination Date [Axis] Non-PEO NEO Non-PEO NEO [Member] Derivative [Table] Accumulated Other Comprehensive Income (Loss) [Table] Other Proceeds from (Payment for) Other Financing Activity Recourse Debt [Member] Recourse Debt [Member] Recourse Debt [Member] Derivative [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Name Trading Arrangement, Individual Name Award Type [Domain] Award Type [Domain] Non-Controlling Interest Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Changes in working capital items Other Noncash Income (Expense) Other Noncash Income (Expense) Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Compensation Amount Outstanding Recovery Compensation Amount Term loan Debt Instrument, Face Amount Dividend yield Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Dividend Rate Statement of Comprehensive Income [Abstract] Total Expenses Operating Costs and Expenses Foreign Exchange Contract [Member] Foreign Exchange Contract [Member] Aircraft spare engines Air Transportation Equipment [Member] Wells Fargo Bank, N.A. Wells Fargo Bank, N.A. [Member] Wells Fargo Bank, N.A. Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Estimate of Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Retirement Plan Type [Domain] Retirement Plan Type [Domain] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Name Awards Close in Time to MNPI Disclosures, Individual Name Weighted average estimated fair value Beginning balance, Weighted Average Grant Date Fair Value Ending balance, Weighted Average Grant Date Fair Value Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Other comprehensive loss attributable to non-controlling interest Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Asset Acquisition [Line Items] Asset Acquisition [Line Items] Revenues Revenues [Abstract] APIC, Share-based Payment Arrangement, Increase for Cost Recognition APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Segments [Domain] Segments [Domain] Award Date [Domain] Award Date [Domain] Performance Shares [Member] Performance Shares [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Pledging Purpose [Domain] Pledging Purpose [Domain] Less: allowance for depreciation Less: allowance for depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Segment profit (loss) Segment Profit Loss Segment profit (loss). Company Selected Measure Name Company Selected Measure Name Fair Value Measurement [Domain] Fair Value Measurement [Domain] Brookfield Brookfield Infrastructure Partners L.P. [Member] Brookfield Infrastructure Partners L.P. Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Net Income (Loss) Available to Common Stockholders, Diluted Net Income (Loss) Available to Common Stockholders, Diluted All Executive Categories All Executive Categories [Member] Stockholders' Equity Note [Abstract] Other Operating Income Other revenue Other Operating Income Common stock, $0.625 par value: Authorized shares — 120,000,000 Issued shares — 67,325,950 and 67,083,149 Outstanding shares — 37,632,377 and 37,895,641 Common Stock, Value, Issued Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Share of affiliates’ earnings, net of dividends Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Income (Loss) from Equity Method Investments, Net of Dividends or Distributions Depreciation expense 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Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Number of years to acquire ownership interest Joint Venture, Potential Ownership Interest To Acquire, Term Joint Venture, Potential Ownership Interest To Acquire, Term Other operating expense Other Cost and Expense, Operating Noncontrolling Interest Noncontrolling Interest [Member] Document Transition Report Document Transition Report Basis of Presentation Accounting Standards Update and Change in Accounting Principle [Text Block] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Underlying Securities Award Underlying Securities Amount Change in component Other Comprehensive Income (Loss), before Reclassifications, before Tax Equity Component [Domain] Equity Component [Domain] Purchases of assets previously leased Payments to Acquire Assets Previously Leased, Investing Activities Payments to Acquire Assets Previously Leased, Investing Activities Document Period End Date Document Period End Date PEO Actually 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Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Additional paid in capital Additional Paid in Capital Rent and other receivables, net Accounts and Other Receivables, Net, Current Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Number of derivative instruments Derivative, Number of Instruments Held Derivative Contract [Domain] Derivative Contract [Domain] Asset Acquisition [Domain] Asset Acquisition [Domain] All Individuals All Individuals [Member] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Asset acquisition, consideration transferred Asset Acquisition, Consideration Transferred Name Forgone Recovery, Individual Name Unrealized gain on derivative instruments Unrealized Gain (Loss) on Derivatives Statistical Measurement [Axis] Statistical Measurement [Axis] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Variable lease revenue Operating Lease, Variable Lease Income Payment for management fee Payment for Management Fee Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Net Income (Loss) Available to Common Stockholders, Basic Net Income (Loss) Available to Common Stockholders, Basic Standby letters of credit [Member] Financial Standby Letter of Credit [Member] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Fair value hedging instruments Schedule of Fair Value Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Receivables, net Accounts Receivable, after Allowance for Credit Loss, Current Title of 12(b) Security Title of 12(b) Security Accumulated Other Comprehensive Income (Loss) [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Other Comprehensive Income, net of taxes Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Treasury stock, shares issued Treasury stock, shares issued, beginning Treasury stock, shares issued, ending Treasury Stock, Common, Shares GATX Share Data Earnings Per Share [Abstract] Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items] Asset Acquisition [Table] Asset Acquisition [Table] Net gains on disposition of owned assets Disposition Gains and Losses on Owned Assets Disposition gains and losses on sales of operating assets Non-dedicated engine revenue Non-dedicated engine revenue Non-dedicated engine revenue Noncontrolling Interest [Abstract] Effect of dilutive securities: Weighted Average Number of Shares Outstanding, Diluted, Adjustment [Abstract] Treasury Stock, Shares, Acquired Treasury Stock, Shares, Acquired Award Timing Disclosures [Line Items] Undistributed Earnings (Loss) Allocated to Participating Securities, Diluted Undistributed Earnings (Loss) Allocated to Participating Securities, Diluted Service cost Defined Benefit Plan, Service Cost Measurement Frequency [Domain] Measurement Frequency [Domain] Operating Assets and Facilities Property, Plant and Equipment Disclosure [Text Block] Net income Net income Net Income Attributable to GATX Net Income (Loss) Attributable to Parent Components of Lease Income Operating Lease, Lease Income [Table Text Block] Portfolio investments and capital additions Portfolio investments and capital additions Cash paid for the acquisition of operating assets Payments to Acquire Investments and Property, Plant, and Equipment Payments to Acquire Investments and Property, Plant, and Equipment Expiration Date Trading Arrangement Expiration Date Recourse Status [Axis] Recourse Status [Axis] Fixed lease revenue Operating Lease, Lease Income, Lease Payments Operating assets and facilities, net Operating assets and facilities, net Property, Plant and Equipment, Net Stock repurchases Payments for Repurchase of Common Stock Adoption Date Trading Arrangement Adoption Date Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Additional lease revenue gatxOperatingLeaseOtherIncome gatxOperatingLeaseOtherIncome Entity Current Reporting Status Entity Current Reporting Status Derivative [Line Items] Derivative [Line Items] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Finance lease revenue Direct Financing Lease, Lease Income Consolidated Entities [Domain] Consolidated Entities [Domain] Retained earnings Retained Earnings (Accumulated Deficit) Locomotive Acquisition Locomotive Acquisition [Member] Locomotive Acquisition Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] GABX GABX [Member] GABX Schedule Of Changes In Noncontrolling Interest Schedule Of Changes In Noncontrolling Interest [Table Text Block] Schedule Of Changes In Noncontrolling Interest Class of Stock [Axis] Class of Stock [Axis] Interest Expense, Operating and Nonoperating Interest Expense, Operating and Nonoperating Net proceeds from issuances of debt with original maturities longer than 90 days Net proceeds from the issuance of debt Proceeds from Issuance of Long-Term Debt Current Fiscal Year End Date Current Fiscal Year End Date Unrealized Loss on Derivative Instruments Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Expected term of stock options and stock appreciation rights, in years Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Statement [Table] Statement [Table] Other (expense) income Other Nonoperating Income (Expense) Derivative liability Derivative Liability Share of affiliates' earnings (pre-tax) Income (Loss) From Equity Method Investment, Before Tax This item represents the entity's proportionate share for the period of the pre-tax income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee. Income (loss) from equity method investment, pre-tax. Deferred income taxes Deferred Income Tax Expense (Benefit) Deferred Income Tax Expense (Benefit) Adjustments to reconcile income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Interest Rate Contract [Member] Interest Rate Contract [Member] Non-Controlling Interest Noncontrolling Interest Disclosure [Text Block] Denominator: Weighted Average Number of Shares Outstanding, Diluted [Abstract] All Adjustments to Compensation All Adjustments to Compensation [Member] Recourse Floating Rate Debt Fair Value Disclosure Recourse Floating Rate Debt Fair Value Disclosure Recourse floating rate debt fair value disclosure. Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Amendment Flag Amendment Flag Tax benefit from share-based compensation expense Share-Based Payment Arrangement, Expense, Tax Benefit Retiree Health and Life [Member] Other Postretirement Benefits Plan [Member] Treasury stock at cost (33,937,924 and 33,916,337 shares) Treasury Stock, Common, Value Termination Date Trading Arrangement Termination Date Net cash (used in) provided by financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Director Shares Director Shares [Member] Director Shares Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Denominator for basic earnings per share — weighted average shares Weighted Average Number of Shares Outstanding, Basic Computation of basic and diluted net income per common share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Segment Reporting [Abstract] Segment Reporting [Abstract] Maintenance expense Cost of Property Repairs and Maintenance Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Operating lease expense Operating Lease, Expense Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Risk-free interest rate Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Entity Tax Identification Number Entity Tax Identification Number Total expenses (1) Costs and Expenses [Abstract] Income tax effect Reclassification from AOCI, Current Period, Tax Asset Acquisition [Axis] Asset Acquisition [Axis] Schedule of Variable Interest Entities Schedule of Variable Interest Entities [Table Text Block] Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Consolidated Entities [Axis] Consolidated Entities [Axis] Common stock, par value Common Stock, Par or Stated Value Per Share Common stock, shares issued Common stock, shares issued, beginning Common stock, shares issued, ending Common Stock, Shares, Issued Derivative Instruments and Hedging Activities Disclosures [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross Guarantor Obligations by Nature [Axis] Guarantor Obligations, Nature [Axis] Dividends Payments of Dividends Payments of Dividends Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Operating Lease, Lease Income Operating Lease, Lease Income Assets and liabilities at fair value recurring basis Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Number of assets acquired Number Of Assets Acquired Number Of Assets Acquired Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Lease Income Total lease revenue Lease revenue Lease Income Total Liabilities Total liabilities Liabilities Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] RailPulse RailPulse [Member] RailPulse Pledging Purpose [Axis] Pledging Purpose [Axis] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Proceeds from sales of other assets Proceeds from Sale of Other Productive Assets Proceeds from Sale of Other Productive Assets Stock Issued During Period, Value, New Issues Stock Issued During Period, Value, New Issues Statement [Line Items] Statement [Line Items] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and Cash Equivalents Cash and cash equivalents Cash and Cash Equivalent Counterparty Name [Axis] Counterparty Name [Axis] Common Stock [Member] Common Stock [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Commercial paper and borrowings under bank credit facilities Other Short-Term Borrowings Net (decrease) increase in Cash, Cash Equivalents, and Restricted Cash during the period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation