GATX (GATX) 10-K 25 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Billions, except Share data in Millions, unless otherwise specified	Dec. 31, 2014	Jan. 31, 2015	Jun. 30, 2014
Document and Entity Information [Abstract]
Entity Registrant Name	GATX Corporation
Entity Central Index Key	40211
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$3
Entity Common Stock, Shares Outstanding		44.3

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Assets
Cash and Cash Equivalents	$209.90	$379.70
Restricted Cash	14.5	20.3
Receivables
Rent and other receivables	86	80.1
Loans	97.3	122.7
Finance leases	174.7	207.3
Less: allowance for losses	-5.7	-5.2
Receivables, net	352.3	404.9
Operating Assets and Facilities
Operating Assets and Facilities ($123.1 and $123.3 related to a consolidated VIE)	8,143.50	7,390.70
Less: allowance for depreciation ($35.0 and $30.3 related to a consolidated VIE)	-2,455.50	-2,320.40
Operating assets and facilities, net	5,688	5,070.30
Investments in Affiliated Companies	357.7	354.3
Goodwill	86.1	94.6
Other Assets	229	225.5
Total Assets	6,937.50	6,549.60
Liabilities and Shareholders’ Equity
Accounts Payable and Accrued Expenses	165.9	159.6
Debt
Commercial paper and borrowings under bank credit facilities	72.1	23.6
Recourse	4,179.90	3,765.90
Nonrecourse ($15.9 and $25.4 related to a consolidated VIE)	-15.9	-72.6
Capital lease obligations	6.3	8.9
Total Debt	4,274.20	3,871
Deferred Income Taxes	937.3	891.4
Other Liabilities	246.1	230.6
Total Liabilities	5,623.50	5,152.60
Shareholders’ Equity
Common stock, $0.625 par value: Authorized shares — 120,000,000 Issued shares — 66,600,984 and 66,349,906 Outstanding shares — 44,198,850 and 45,868,698	-41.4	-41.3
Additional paid in capital	-672.8	-668.9
Retained earnings	1,501.70	1,358.40
Accumulated other comprehensive loss	148.4	42.7
Treasury stock at cost (22,402,134 and 20,481,208 shares)	-753.5	-628.9
Total Shareholders’ Equity	1,314	1,397
Total Liabilities and Shareholders’ Equity	$6,937.50	$6,549.60

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
VIE for Rail	$8,143.50	$7,390.70
VIE depreciation allowance	2,455.50	2,320.40
VIE nonrecourse debt	15.9	72.6
Common stock, par value	$0.63	$0.63
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	66,600,984	66,349,906
Common stock, shares outstanding	44,198,850	45,868,698
Treasury stock, shares outstanding	22,402,134	20,118,120
Variable Interest Entity, Primary Beneficiary [Member]
VIE for Rail	123.1	123.3
VIE depreciation allowance	35	30.3
VIE nonrecourse debt	$15.90	$25.40

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Revenues
Lease revenue	$1,086.60	$975.20		$917
Marine operating revenue	286.3	275.1		265.5
Other revenue	78.1	70.7		60.7
Total Revenues	1,451	1,321		1,243.20
Expenses
Maintenance expense	337	294		269.7
Marine operating expense	197.8	189.8		182.4
Depreciation	273.5	255		237.4
Operating lease expense	108.7	129.4		130.2
Other operating expense	28.9	26.1		24.2
Selling, general and administrative	189.2	178.3		160.2
Total Expenses	1,135.10	1,072.60		1,004.10
Other Income (Expense)
Net gain on asset dispositions	87.2	85.6		79.5
Interest expense, net	-158.4	-166.6		-166.6
Other (expense) income	-13.5	-8.4		-8.2
Income before Income Taxes and Share of Affiliates’ Earnings	231.2	159		143.8
Income Taxes	-75.7	-65.5		-26.1
Share of Affiliates’ Earnings (net of tax)	49.5	75.8		19.6
Net Income	205	169.3		137.3
Other Comprehensive Income, net of taxes
Foreign currency translation adjustments	79.1	-25.8		-25
Unrealized gain (loss) on securities	0.1	-0.8		-0.2
Unrealized gain (loss) on derivative instruments	-3	-22.4		-11.7
Post-retirement benefit plans	-29.5	52.9		-12.4
Other comprehensive income (loss)	-105.7	101.9		24.5
Comprehensive Income	$99.30	$271.20		$161.80
Share Data
Basic earnings per share (in dollars per share)	$4.55	$3.64	[1]	$2.93
Average number of common shares (in shares)	45	46.4		46.8
Diluted earnings per share (in dollars per share)	$4.48	$3.59	[1]	$2.88
Average number of common shares and common share equivalents (in shares)	45.8	47.1		47.6
Dividends declared per common share (in dollars per share)	$1.32	$1.24		$1.20
[1]	(1)Quarterly earnings per share may not be additive, as per share amounts are computed independently for each quarter and the full year is based on the respective weighted average common shares and common stock equivalents outstanding.

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net income	$205	$169.30	$137.30
Adjustments to reconcile income to net cash provided by operating activities:
Gains on sales of assets	-79.3	-80.7	-61.4
Depreciation	287	267.8	249.4
Share-based Compensation	14	13.1	12.2
Asset impairment charges	1.3	5.9	5
Deferred income taxes	61.4	53.6	24.4
Share of affiliates’ earnings, net of dividends	-9.5	-41.4	15.5
Change in income taxes payable	-4.4	4.5	-9.4
Change in accrued operating lease expense	-5.2	-7.7	-11
Employee benefit plans	3.7	7.5	0.8
Other	-24.8	8.8	7.4
Net cash provided by operating activities	449.2	400.7	370.2
Investing Activities
Additions to operating assets and facilities	-1,015.20	-744.1	-739.3
Loans extended	0	-14.2	-1
Investments in affiliates	-15.3	-101.3	-29.7
Portfolio investments and capital additions	-1,030.50	-859.6	-770
Purchases of leased-in assets	-150.5	-61.4	-1.3
Portfolio proceeds	264	385.3	288.9
Proceeds from sales of other assets	26.9	32.3	28.4
Proceeds from sale-leasebacks	0	90.7	104.9
Net decrease (increase) in restricted cash	5.8	9.5	5.5
Payments for (Proceeds from) Other Investing Activities	5.8	0	0
Net cash used in investing activities	-878.5	-403.2	-343.6
Financing Activities
Net proceeds from issuances of debt (original maturities longer than 90 days)	1,223	1,132.20	445.2
Repayments of debt (original maturities longer than 90 days)	-819.8	-602.8	-671.2
Net increase (decrease) in debt with original maturities of 90 days or less	50	-251.3	243.3
Payments on capital lease obligations	-2.6	-2.4	-3
Stock repurchases	-124.6	-68.6	0
Dividends	-62	-60.5	-58.8
Other	-1.8	2.5	4.6
Net cash (used in) provided by financing activities	262.2	149.1	-39.9
Effect of Exchange Rate Changes on Cash and Cash Equivalents	-2.7	-1.1	-0.9
Net (decrease) increase in Cash and Cash Equivalents during the period	-169.8	145.5	-14.2
Cash and Cash Equivalents at beginning of period	379.7	234.2	248.4
Cash and Cash Equivalents at end of period	$209.90	$379.70	$234.20

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity (USD $)	Total	Common stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
In Millions, except Share data, unless otherwise specified
Balance at beginning of period at Dec. 31, 2010
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			-19,100,000
Other comprehensive income (loss)						$24.50
Balance at end of period at Dec. 31, 2011			-560.3	644.4	1,171.20	-169.1
Balance at beginning of period, Common Stock at Dec. 31, 2011		41.1
Balance at beginning of year at Dec. 31, 2011		65,800,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			-19,100,000
Issuance of common stock, Shares		200,000
Issuance of common stock		0.1		2.9
Stock repurchases, Shares	0
Stock repurchases	0
Share-based compensation effects				11.2
Net income	137.3				137.3
Dividends declared					-59.1
Other comprehensive income (loss)	24.5
Balance at end of period at Dec. 31, 2012	1,244.20		-560.3	658.5	1,249.40	-144.6
Balance at end of period, Common Stock at Dec. 31, 2012		41.2
Balance at end of period, Common Stock, Shares at Dec. 31, 2012		66,000,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			-20,500,000
Issuance of common stock, Shares		300,000
Issuance of common stock		0.1		1.1
Stock repurchases, Shares	1,400,000
Stock repurchases	-68.6
Share-based compensation effects				9.3
Net income	169.3				169.3
Dividends declared					-60.3
Other comprehensive income (loss)	101.9					101.9
Balance at end of period at Dec. 31, 2013	1,397		-628.9	668.9	1,358.40	-42.7
Balance at end of period, Common Stock at Dec. 31, 2013	41.3	41.3
Balance at end of period, Common Stock, Shares at Dec. 31, 2013	66,349,906	66,300,000
Balance at beginning of period at Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			-20,500,000
Net income	53.3
Balance at end of period at Dec. 31, 2013	1,397		-628.9	668.9	1,358.40
Balance at end of period, Common Stock at Dec. 31, 2013	41.3	41.3
Balance at end of period, Common Stock, Shares at Dec. 31, 2013	66,349,906	66,300,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			-22,400,000
Issuance of common stock, Shares		300,000
Issuance of common stock		0.1		0
Stock repurchases, Shares	1,900,000
Stock repurchases	-124.6
Share-based compensation effects				3.9
Net income	205
Dividends declared					-61.7
Other comprehensive income (loss)	-105.7
Balance at end of period at Dec. 31, 2014	1,314		-753.5	672.8	1,501.70	-148.4
Balance at end of period, Common Stock at Dec. 31, 2014	41.4	41.4
Balance at end of period, Common Stock, Shares at Dec. 31, 2014	66,600,984	66,600,000
Balance at beginning of period at Sep. 30, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period, Shares			-22,400,000
Net income	58.5
Balance at end of period at Dec. 31, 2014	1,314		-753.5			-148.4
Balance at end of period, Common Stock at Dec. 31, 2014	$41.40
Balance at end of period, Common Stock, Shares at Dec. 31, 2014	66,600,984

Description_of_Business

Description of Business	12 Months Ended
	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business
	As used herein, "GATX," "we," "us," "our," and similar terms refer to GATX Corporation and its subsidiaries, unless indicated otherwise.
	We lease, operate, manage, and remarket long-lived, widely-used assets, primarily in the rail and marine markets. We also invest in joint ventures that complement our existing business activities. We report our financial results through four primary business segments: Rail North America, Rail International, American Steamship Company (“ASC”), and Portfolio Management.

Accounting_Changes

Accounting Changes	12 Months Ended
	Dec. 31, 2014
Accounting Changes and Error Corrections [Abstract]
Accounting Changes	Change in Accounting Estimate
	During the first quarter of 2014, we completed a review of the estimated useful lives used for our North American railcar fleet and determined that the economic service life of many of our railcars differed from the useful life currently used to calculate depreciation. As a result, effective January 1, 2014, we revised the estimated useful lives from a range of 30-38 years to a range of 27-42 years. In aggregate, the average depreciable life of the fleet increased approximately 2.2 years. The impacts of these implemented changes on depreciation expense for affected assets was a net decrease in depreciation expense of approximately $21.9 million and an increase in net income of $14.0 million, or $0.31 per diluted share for the year ended December 31, 2014.
	New Accounting Pronouncements
	Discontinued Operations
	In April 2014, the Financial Accounting Standards Board ("FASB") issued amendments to authoritative guidance for reporting discontinued operations and disposals of components of an entity. The amendments require that disposals representing strategic shifts that have (or will have) a major effect on an entity’s operations or financial results should be reported in discontinued operations. The amendments also expand the disclosure requirements for both discontinued operations and significant dispositions that do not qualify as discontinued operations.
	The amendments are effective for us beginning in the first quarter of 2015. Adoption of the new guidance is not expected to impact the amount or timing of net income but may result in changes to the presentation and disclosures of our financial statements.
	Revenue from Contracts with Customers
	In May 2014, the FASB issued authoritative accounting guidance that supersedes most current revenue recognition guidance, including industry-specific guidance. The new guidance requires companies to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration it expects to be entitled to in exchange for those goods or services.
	The guidance is effective for us beginning in the first quarter of 2017, and early adoption is not permitted. We can adopt the new guidance using either the retrospective method or the cumulative effect transition method. We are still evaluating the effect that the new guidance will have on our consolidated financial statements and related disclosures, including which transition method we will use.

Significant_Accounting_Policie

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies
	Basis of Presentation
	We prepared the accompanying consolidated financial statements in accordance with US GAAP. Certain prior year amounts may have been reclassified to conform to the 2014 presentation.
	Use of Estimates
	Preparing financial statements in accordance with GAAP requires us to make estimates and assumptions that affect the amounts we report. We regularly evaluate our estimates and judgments based on historical experience and other relevant facts and circumstances. Actual amounts could differ from our estimates.
	Consolidation
	Our consolidated financial statements include our assets, liabilities, revenues, and expenses, as well as the assets, liabilities, revenues, and expenses of subsidiaries in which we have a controlling financial interest and variable interest entities for which we are the primary beneficiary. We have eliminated intercompany transactions and balances. Our consolidated subsidiaries include the following wholly owned, bankruptcy-remote special purpose corporations that finance and lease railcars: General American Railcar Corporation, General American Railcar Corporation III, General American Marks Company, and GARC LLC. The debt and lease obligations of these special purpose corporations are nonrecourse to us, and their assets are available first to satisfy claims of their creditors.
	Investments in Affiliates
	We use the equity method to account for investments in joint ventures and other unconsolidated entities if we have the ability to exercise significant influence over the financial and operating policies of those investees. Under the equity method, we record our initial investments in these entities at cost and subsequently adjust the investment for our share of the affiliates’ undistributed earnings (losses), and distributions. We include loans to and from affiliates as part of our investment in the affiliate and include interest on any such loans in our share of the affiliates’ earnings. We review the carrying amount of our investments in affiliates annually, or whenever circumstances indicate that the value of these investments may have declined. If we determine an investment is impaired on an other-than-temporary basis, we record a loss equal to the difference between the fair value of the investment and its carrying value. See "Note 7. Investments in Affiliated Companies."
	Variable Interest Entities
	We evaluate whether an entity is a variable interest entity based on the sufficiency of the entity’s equity and by determining whether the equity holders have the characteristics of a controlling financial interest. To determine if we are the primary beneficiary of a variable interest entity, we assess whether we have the power to direct the activities that most significantly impact the economic performance of the entity as well as the obligation to absorb losses or the right to receive benefits that may be significant to the entity. These determinations are both qualitative and quantitative, and they require us to make judgments and assumptions about the entity’s forecasted financial performance and the volatility inherent in those forecasted results. We evaluate new investments for variable interest entity determination and regularly review all existing entities for events that may result in an entity becoming a variable interest entity or us becoming the primary beneficiary of an existing variable interest entity. See "Note 8. Variable Interest Entities."
	Fair Value Measurements
	Fair value is the price that a market participant would receive to sell an asset or pay to transfer a liability in an orderly transaction at the measurement date. We classify fair value measurements according to the three-level hierarchy defined by GAAP, and those classifications are based on our judgment about the reliability of the inputs we use in the fair value measurement. Level 1 inputs are quoted prices available in active markets for identical assets or liabilities. Level 2 inputs are observable, either directly or indirectly, and may include quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data. For assets or liabilities with a specified contractual term, Level 2 inputs must be observable for substantially the full term of that asset or liability. Level 3 inputs are unobservable, meaning they are supported by little or no market activity. Fair value measurements classified as Level 3 typically rely on pricing models and discounted cash flow methodologies, both of which require significant judgment. See "Note 10. Fair Value Disclosure."
	Cash and Cash Equivalents
	We classify all highly liquid investments with a maturity of three months or less when purchased as cash equivalents.
	Restricted Cash
	Restricted cash is cash and cash equivalents that are restricted as to withdrawal and use. Our restricted cash primarily relates to contractually required cash amounts we maintain for two wholly owned bankruptcy-remote, special purpose corporations.
	Operating Assets and Facilities
	We state operating assets, facilities, and capitalized improvements at cost. We include assets we acquire under capital leases in operating assets, and we record the related obligations as liabilities. We depreciate operating assets and facilities over their estimated useful lives or lease terms to estimated residual values using the straight-line method. We depreciate leasehold improvements over the shorter of their useful lives or the lease term. Our estimated depreciable lives of operating assets and facilities are as follows:
	Railcars	27–42 years
	Locomotives	10–20 years
	Buildings	40–50 years
	Leasehold improvements	5–15 years
	Marine vessels	30–65 years
	Other equipment	5–30 years
	We review long-lived assets for impairment whenever circumstances indicate that the carrying amount of those assets may not be recoverable. We evaluate the recoverability of assets to be held and used by comparing the carrying amount of the asset to the undiscounted future net cash flows we expect the asset to generate. If we determine an asset is impaired, we recognize an impairment loss equal to the amount the carrying amount exceeds the asset’s fair value. We classify assets we plan to sell or otherwise dispose of as held for sale, provided they meet specified accounting criteria, and we record those assets at the lower of their carrying amount or fair value less costs to sell.
	Lease Classification
	We determine the classification of a lease at its inception. If the provisions of the lease subsequently change, other than by renewal or extension, we evaluate whether that change would have resulted in a different lease classification had the change been in effect at inception. If so, the revised agreement is considered a new lease for lease classification purposes. See "Note 5. Leases."
	Operating Leases
	We offer full-service and net operating leases. We price full-service leases as an integrated service that includes amounts related to executory costs, such as maintenance, insurance, and ad valorem taxes. We do not offer stand-alone maintenance service contracts and are unable to separate executory costs from full-service lease revenue. We recognize operating lease revenue, including amounts related to executory costs, on a straight-line basis over the term of the underlying lease. As a result, we may not recognize lease revenue in the same period as maintenance and other executory costs, which we expense as incurred. See "Note 5. Leases."
	Finance Leases
	For finance leases, we record a gross lease payment receivable and an estimated residual value, net of unearned income. For sales-type leases, we may also recognize a gain or loss in the period the lease is recorded. Gross lease payment receivables are the rents we expect to receive through the end of the lease term for a leased asset. Estimated residual values are our estimates of value of an asset at the end of a finance lease term. We review our estimates of residual values annually or whenever circumstances indicate that residual values may have declined. Other-than-temporary declines in value are recognized as impairments. Initial unearned income is the amount that the original lease payment receivable and the estimated residual value of the leased asset exceeds the original cost or carrying value of the leased asset. We amortize unearned income to lease revenue using the interest method, which produces a constant yield over the lease term. We also defer the initial direct costs related to our direct finance leases and amortize those costs over the lease term as an adjustment to lease revenue.
	We regularly review the finance lease portfolio and classify finance leases as non-performing if it is probable that we will be unable to collect all amounts due under the lease. We generally stop accruing income on non-performing finance leases until all contractual payments are current. We apply payments we receive for non-performing finance leases to the lease payment receivable. See "Note 5. Leases."
	Inventory
	Our inventory consists of railcar and locomotive repair components and marine vessel spare parts. All inventory balances are stated at lower of cost or market. Railcar repair components are valued using the average cost method. Vessel spare parts inventory is valued using the first-in, first-out method. Inventory is included in other assets on the balance sheet.
	Loans
	We record loans at their principal amount outstanding adjusted for allowances, deferred fees, unamortized premiums or discounts, and accrued interest. We review the loan portfolio regularly and classify a loan as impaired when it is probable that we will be unable to collect all amounts due under the loan agreement. Since most loans are collateralized, we generally measure impairment as the amount the carrying value of the loan exceeds the expected repayments, including any value attributable to underlying collateral. We do not typically recognize interest income on impaired loans until the loan has been paid to contractually current status. We offset loan origination fees by the related direct loan origination costs for a given loan and amortize the net amount of those costs over the term of the loan as an adjustment to interest income. See "Note 6. Loans."
	Allowance for Losses
	The allowance for losses is our estimate of credit losses associated with reservable assets. Reservable assets are divided into two categories: rent and other receivables, which includes short-term trade billings, and loans and finance lease receivables. We base our loss reserves for rent and other receivables on historical loss experience and judgments about the impact of economic conditions, the state of the markets we operate in, and collateral values, if applicable. In addition, we may establish specific reserves for known troubled accounts. We evaluate reserve estimates for loans and finance lease receivables on a customer-specific basis, considering each customer's particular credit situation. We also consider the factors we use to evaluate rent and other receivables, which are outlined above. We charge amounts against the allowance when we deem them uncollectable. We made no material changes in our estimation methods or assumptions for the allowance during 2014. We believe that the allowance is adequate to cover losses inherent in our reservable assets as of December 31, 2014. Since the allowance is based on judgments and estimates, it is possible that actual losses incurred will differ from the estimate. See "Note 18. Allowance for Losses."
	Goodwill
	We recognize goodwill when the consideration paid to acquire a business exceeds the fair value of the net assets acquired.  We assign goodwill to the same reporting unit as the net assets of the acquired business and we assess our goodwill for impairment on an annual basis in the fourth quarter, or during interim periods if impairment indicators are present. If the carrying amount of the applicable reporting unit exceeds its fair value, we compare the implied fair value of the reporting unit’s goodwill with the carrying amount of goodwill. We record an impairment loss if the carrying amount of goodwill exceeds its implied fair value. The fair values of our reporting units are determined using discounted cash flow models. See "Note 17. Goodwill."
	Income Taxes
	We calculate provisions for federal, state, and foreign income taxes on our reported income before income taxes. We base our calculations of deferred tax assets and liabilities on the differences between the financial statement and tax bases of assets and liabilities, using enacted rates in effect for the year we expect the differences will reverse. We reflect the cumulative effect of changes in tax rates from those we previously used to determine deferred tax assets and liabilities in the provision for income taxes in the period the change is enacted. Provisions for income taxes in any given period differ from those currently payable or receivable because certain items of income and expense are recognized in different periods for financial reporting purposes than for income tax purposes. We may deduct expenses or defer income attributable to uncertain tax positions for tax purposes, however, we have not recognized a tax benefit in the financial statements for those items. We include our liability for uncertain tax positions in other liabilities on the balance sheet. See "Note 13. Income Taxes."
	Derivatives
	We use derivatives, such as interest rate swap agreements, Treasury rate locks, options, and currency forwards, to hedge our exposure to interest rate and foreign currency exchange rate risk on existing and anticipated transactions. We formally designate derivatives that meet specific accounting criteria as qualifying hedges at inception. These criteria require us to have the expectation that the derivative will be highly effective at offsetting changes in the fair value or expected cash flows of the hedged exposure, both at the inception of the hedging relationship and on an ongoing basis.
	We recognize all derivative instruments at fair value and classify them on the balance sheet as either other assets or other liabilities. We generally base the classification of derivative activity in the statements of comprehensive income and cash flows on the nature of the hedged item. For derivatives we designate as fair value hedges, we recognize changes in the fair value of both the derivative and the hedged item in earnings. For derivatives we designate as cash flow hedges, we record the effective portion of the change in the fair value of the derivative as part of other comprehensive income (loss), and we recognize those changes in earnings in the period the hedged transaction affects earnings. We recognize any ineffective portion of the change in the fair value of the derivative immediately in earnings. Although we do not hold or issue derivative financial instruments for purposes other than hedging, we do not designate certain derivatives as accounting hedges. We recognize changes in the fair value of these derivatives in earnings immediately. We classify gains and losses on derivatives that are not designated as hedges as other expenses, and we include the related cash flows in cash flows from operating activities. See "Note 10. Fair Value Disclosure."
	Defined Benefit Pension and Other Post-Retirement Plans
	Our balance sheet reflects the funded status of our pension and post-retirement plans, which is the difference between the fair value of the plan assets and the projected benefit obligation. We recognize the aggregate overfunding of any plans in other assets, the aggregate underfunding of any plans in other liabilities, and the corresponding adjustments for unrecognized actuarial gains (losses) and prior service cost (credits) in accumulated other comprehensive income (loss). See "Note 11. Pension and Other Post-Retirement Benefits."
	Foreign Currency
	We translate the assets and liabilities of our operations that have non-US dollar functional currencies at exchange rates in effect at year-end. Revenue, expenses, and cash flows are translated monthly using average exchange rates. We defer gains and losses resulting from foreign currency translation and record those gains and losses as a separate component of accumulated other comprehensive income (loss). Gains and losses resulting from foreign currency transactions and from the remeasurement of non-functional currency assets and liabilities are recorded net of related hedges in other expense during the periods in which they occur. Net (losses) gains were $(3.4) million, $2.1 million and $0.5 million for 2014, 2013, and 2012.
	Environmental Liabilities
	We record accruals for environmental remediation costs at sites relating to past or discontinued operations when they are probable and when we can reasonably estimate the expected costs. We record adjustments to initial estimates as necessary. Since these accruals are based on estimates, actual environmental remediation costs may differ. We expense or capitalize environmental remediation costs related to current or future operations as appropriate. See "Note 23. Legal Proceedings and Other Contingencies."
	Marine Operating Revenue
	We recognize marine operating revenue as we perform shipping services, and we allocate revenue among reporting periods based on the relative transit time in each reporting period for shipments in process.
	Other Revenue
	We include customer liability repair revenue, fee income, interest on loans, and other miscellaneous revenues in other revenue. We recognize these revenues when earned, which, in the case of management fees we receive from affiliates, is when we perform the related services.
	Interest Expense, net
	Interest expense is the interest we accrue on indebtedness and the amortization of debt issuance costs and debt discounts. We defer debt issuance costs and discounts and amortize them over the term of the related debt. We report interest expense net of interest income on bank deposits. Interest income on bank deposits was $0.9 million in 2014, $1.2 million in 2013, and $1.9 million in 2012.
	Operating Lease Expense
	We classify leases of certain railcars and other assets and facilities, such as maintenance facilities and equipment, as operating leases. We record the lease expense associated with these leases on a straight-line basis. We defer gains and financing costs associated with sale-leasebacks and amortize those gains and costs as a component of operating lease expense over the related leaseback term. We also classify our leases of office facilities and related administrative assets as operating leases, and we record the associated expense in selling, general and administrative expense. See "Note 5. Leases."
	Maintenance and Repair Costs
	We expense maintenance and repair costs as incurred. We capitalize certain costs incurred in connection with planned major maintenance activities if those activities improve the asset or extend its useful life. We depreciate those capitalized costs over the estimated useful life of the improvement. We capitalize required regulatory survey costs for vessels and amortize those costs over the applicable survey period, which is generally five years.
	ASC Expense Seasonality
	ASC's sailing season runs from April 1 to December 31 of each year. We defer certain indirect expenses incurred prior to the beginning of the sailing season, such as winter maintenance, insurance, operating lease expense, and depreciation and amortize them ratably over the sailing season.
Share-Based Compensation
We base our measurement of share-based compensation expense on the grant date fair value of an award, and we recognize the expense net of estimated forfeitures over the requisite service period. Forfeiture rates at grant date are initially based on historical experience and are adjusted in subsequent periods if actual experience differs from the estimate. We record a final adjustment when those awards vest. See "Note 12. Share-Based Compensation."
Net Gain on Asset Dispositions
Net gain on disposition includes gains on sales of operating assets and residual sharing income, which we also refer to as asset remarketing income; non-remarketing disposition gains, primarily from scrapping of railcars; and asset impairment losses. We recognize disposition gains, including non-remarketing gains, upon completion of the sale or scrapping of operating assets. Residual sharing income includes fees we receive from the sale of managed assets and assets subject to residual value guarantees, and we recognize these fees upon completion of the underlying transactions.
The following table presents the net gain on asset dispositions for the years ending December 31 (in millions):
	2014			2013			2012
Disposition gains	$	63.1		$	60		$	42.7
Residual sharing income	9.4			10.8			22.6
Non-remarketing disposition gains	16			20.7			19.2
Asset impairment losses	(1.3		)	(5.9		)	(5.0		)
Net Gain on Asset Dispositions	$	87.2		$	85.6		$	79.5
Other Income (Expense)
We include fair value adjustments on certain financial instruments, gains and/or losses on foreign currency transactions and remeasurements, legal defense costs and litigation settlements, along with other miscellaneous income and expense items in other income (expense).

Supplemental_Cash_Flow_and_Non

Supplemental Cash Flow and Noncash Investing Transactions	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow and Noncash Investing Transaction	Supplemental Cash Flow Information and Noncash Investing Transactions
		2014		2013		2012
	Supplemental Cash Flow Information (in millions)
	Interest paid (1)	$	142.6	$	148.7	$	162.3
	Income taxes paid, net	18.7		7.4		11.1
	________
	-1	Interest paid consisted of interest on debt obligations, interest rate swaps (net of interest received), and capital leases. The interest expense we capitalized as part of the cost of construction of major assets was immaterial for all periods presented.
		2014		2013		2012
	Noncash Investing Transactions (in millions)
	Distributions from affiliates (1)	$	1.1	$	174.7	$	—
	Portfolio proceeds (2)	—		91.1		—
	________
	-1	In 2014, we received distributions of 62 railcars with a fair value of $1.1 million from our Southern Capital Corporation LLC affiliate ("SCC"). In 2013, we received five vessels and related working capital with a fair value of $151.8 million in connection with our disposition of the Singco Gas Pte, Limited ("Singco") and Somargas II Pte Limited ("Somargas") joint ventures. Additionally, we received distributions of 640 railcars with a fair value of $22.9 million from SCC.
	-2	Proceeds from the sale of our interest in Ahaus Alstätter Eisenbahn Cargo AG (“AAE”) included receipt of a €67.5 million ($91.1 million) note.
	For additional information see "Note 7. Investments in Affiliated Companies."

Leases

Leases	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Leases	GATX as Lessor
	The following table shows the components of our direct finance leases as of December 31 (in millions):
		2014			2013
	Total contractual lease payments receivable	$	204.8		$	270.2
	Estimated unguaranteed residual value of leased assets	68.5			79.8
	Unearned income	(98.6		)	(142.7		)
	Finance leases	$	174.7		$	207.3
	Leveraged lease revenue
	We had no leveraged leases in 2014 and 2013. Revenue from leveraged leases (net of taxes) was $0.2 million in 2012.
	Usage rents
	We base lease revenue for certain operating leases on equipment usage. Lease revenue from such usage rents was $83.9 million in 2014, $21.3 million in 2013, and $18.2 million in 2012. The increase in 2014 was due to higher utilization revenue as a result of the acquisition of approximately 18,500 boxcars in March, 2014.
	Initial direct costs
	Deferred initial direct costs related to direct financing leases were $0.3 million at December 31, 2014 and $0.4 million, at December 31, 2013.
	Future receipts
	The following table shows our future contractual receipts from finance leases and noncancelable operating leases as of December 31, 2014 (in millions):
		Finance Leases			Operating Leases (1)			Total
	2015	$	26.3		$	923.4		$	949.7
	2016	25.2			740.3			765.5
	2017	23.9			584.1			608
	2018	22.2			464.7			486.9
	2019	11.8			370			381.8
	Years thereafter	95.4			770.4			865.8
		$	204.8		$	3,852.90		$	4,057.70
	__________
	-1	The future contractual receipts due under our full-service operating leases include executory costs such as maintenance, car taxes, and insurance.
	GATX as Lessee
	Capital Lease Assets
	The following table shows assets we financed with capital lease obligations as of December 31 (in millions):
		2014			2013
	Marine vessels	$	83.1		$	81.4
	Less: allowance for depreciation	(75.3		)	(71.4		)
		$	7.8		$	10
	Operating Leases
	We lease assets that are closely associated with our revenue generating operations. At December 31, 2014 we leased approximately 23,000 railcars at Rail North America and one vessel at ASC. In addition, we lease office facilities and other general purpose equipment. Total operating lease expense, which includes amounts recorded in selling, general and administrative expense, was $112.9 million in 2014, $134.0 million in 2013, and $133.3 million in 2012.
	Lease Obligations
	For some leases, we have the option to renew the leases or purchase the assets at the end of the lease term. The specific terms of the renewal and purchase options vary, and we did not include these amounts in our future contractual rental payments. Additionally, the contractual rental payments do not include amounts we are required to pay for licenses, taxes, insurance, and maintenance. The following table shows our future contractual rental payments due under noncancelable leases as of December 31, 2014 (in millions):
		Capital			Recourse			Nonrecourse
		Leases			Operating			Operating
					Leases			Leases (1)
	2015	$	3.1		$	86.3		$	11
	2016	2.7			89			8.1
	2017	1.1			94.2			9.5
	2018	—			85.6			9
	2019	—			81.5			9.7
	Years thereafter	—			310.1			18.7
		$	6.9		$	746.7		$	66
	Less: amounts representing interest	(0.6		)
	Present value of future contractual capital lease payments	$	6.3
	__________
	(1) The amounts shown are primarily the rental payments of one wholly owned, bankruptcy-remote special purpose corporations. We consolidate these rentals for accounting purposes, but they are not our legal obligations.

Investments_in_Affiliated_Comp

Investments in Affiliated Companies	12 Months Ended
	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Investments in Affiliated Companies	Investments in affiliated companies represent investments in and loans to domestic and foreign affiliates, and primarily include companies offering lease financing and related services for customers operating rail and marine assets, as well as companies that lease aircraft engines. Loan amounts included in investments in affiliated companies were $16.3 million as of December 31, 2014 and $24.2 million as of December 31, 2013.
	In 2014, we sold our investments in the Intermodal Investment Fund V and Intermodal Investment Fund VII affiliates. As a result of these sales, we received aggregate cash proceeds of $18.3 million.
	In 2013, we dissolved our Singco and Somargas marine affiliates, taking direct ownership of five liquefied gas carrying vessels with a fair value of $151.8 million. In connection with the dissolution we paid $101.3 million, primarily to satisfy our share of the affiliates' external debt, and recognized a pretax gain of $2.5 million, which is recorded in share of affiliates' earnings. The vessels continue to operate in a vessel pooling arrangement that our former partner manages.
	In 2013, we sold our 37.5% interest in AAE to our partner, Ahaus Alstätter Eisenbahn Holding AG (“AAE Holding”), and recognized a pretax gain of $9.3 million, which we reported as part of our share of affiliates' earnings. The sale price of $114.1 million consisted of a cash payment at closing of $23.0 million and a seller loan of €67.5 million ($91.1 million) at a market interest rate. The loan was paid in full in January 2015.
	In 2012, our gas compression equipment leasing affiliate, Enerven Compression, LLC ("Enerven"), sold substantially all of its assets and is in the process of liquidating. In connection with the disposition, we recognized an impairment loss of $14.8 million in 2012, which we recorded in our share of affiliates' earnings. In 2013, we reversed $1.1 million of the prior impairment loss due to higher than expected proceeds from the asset sales.
	The following table presents our most significant investments in affiliated companies and our ownership percentage in those companies by segment as of December 31, 2014 (in millions):
		Segment		Investment				Percentage
								Ownership
	Rolls-Royce & Partners Finance (1)	Portfolio Management		$	293.6			50	%
	Cardinal Marine Investments LLC	Portfolio Management		45.1				50	%
	Adler Funding LLC	Rail North America		16.9				12.5	%
	Other affiliates	Various		2.1				Various
	Investments in Affiliated Companies			$	357.7
	__________
	(1) Combined investment balances of fourteen separate joint ventures (collectively, the "RRPF affiliates").
	The following table shows our share of affiliates’ earnings by segment for the years ending December 31 (in millions):
		2014				2013				2012
	Rail North America	$	7.9			$	10.3			$	6.5
	Rail International	(0.3		)		21.1				(18.3		)
	Portfolio Management	60.2				60.9				33.4
	Share of affiliates' earnings (pretax)	67.8				92.3				21.6
	Income taxes	(18.3		)		(16.5		)		(2.0		)
	Share of Affiliates' Earnings	$	49.5			$	75.8			$	19.6
	The following table shows our cash investments in and distributions from our affiliates by segment for the years ended December 31 (in millions):
		Cash Investments											Cash Distributions (1)
		2014				2013				2012			2014		2013		2012
	Rail North America	$	—			$	—			$	—		$	20	$	—	$	14.9
	Rail International	—				—				—			—		—		—
	Portfolio Management	15.3				101.3				29.7			34.2		47		38.3
		$	15.3			$	101.3			$	29.7		$	54.2	$	47	$	53.2
	__________
	-1	Cash distributions exclude proceeds from sales of affiliates of $19.4 million in 2014, $55.6 million in 2013, and $12.5 million in 2012.
	Summarized Financial Data of Affiliates
	The following table shows the aggregated operating results for the years ended December 31 for the affiliated companies we held at December 31 (in millions):
		2014				2013				2012
	Revenues	$	339			$	334.5			$	651.8
	Gains on sales of assets	33.7				43.5				57.4
	Net income	99.6				108.6				75.3
	The following table shows aggregated summarized balance sheet data for our affiliated companies as of December 31 (in millions):
		2014				2013
	Current assets	$	211.6			$	200.5
	Noncurrent assets	3,195.10				2,989.20
	Total assets	$	3,406.70			$	3,189.70
	Current liabilities	$	378.4			$	159.6
	Noncurrent liabilities	2,388.20				2,408.80
	Shareholders’ equity	640.1				621.3
	Total liabilities and shareholders' equity	$	3,406.70			$	3,189.70
	Summarized Financial Data for the RRPF Affiliates
	As noted above, our affiliate investments include 50% interests in each of the RRPF affiliates, a collection of fourteen domestic and foreign joint ventures with Rolls-Royce plc (or affiliates thereof, collectively “Rolls-Royce”), a leading manufacturer of commercial aircraft jet engines. The RRPF affiliates are primarily engaged in two business activities: lease financing of aircraft engines to a diverse group of commercial aircraft operators worldwide and lease financing of aircraft engines to Rolls-Royce for use in their engine maintenance programs. In aggregate, the RRPF affiliates own 433 aircraft engines at December 31, 2014 which are generally depreciated over a useful life of 25 years to an estimated residual value. Lease terms vary but typically range from 7 to 10 years. Rolls-Royce manages each of the RRPF affiliates and also performs substantially all required maintenance activities. Our share of affiliates' earnings (after-tax) from the RRPF affiliates was $42.2 million in 2014, $46.5 million in 2013, and $36.7 million in 2012.
	We derived the following financial information from the combined financial statements of the RRPF affiliates.
	The following table shows condensed income statements of the RRPF affiliates for the years ending December 31 (in millions):
		2014				2013				2012
	Lease revenue from third parties	$	176.9			$	147.6			$	140.4
	Lease revenue from Rolls-Royce	124.7				119.7				112.9
	Depreciation expense	(140.7		)		(120.2		)		(115.1		)
	Interest expense	(59.5		)		(65.8		)		(64.8		)
	Other expenses	(11.8		)		(10.2		)		(16.3		)
	Gains on sales of assets	22.7				35.2				35.9
	Income before income taxes	112.3				106.3				93
	Income tax provision (benefits) (1)	(17.3		)		0.4				(3.8		)
	Net income	$	95			$	106.7			$	89.2
	_________
	(1) Represents income taxes directly attributable to the RRPF affiliates in the United Kingdom. Several of the RRPF affiliates are flow through entities and income taxes are incurred at the shareholder level. Amounts shown for 2013 and 2012 include tax benefits of approximately $15.2 million and $9.2 million, attributable to statutory rate decreases in the United Kingdom.
	The following table shows the condensed balance sheets of the RRPF affiliates as of December 31 (in millions):
	2014				2013
Current assets	$	146.3			$	151
Noncurrent assets, including operating assets, net of accumulated depreciation of $862.8 and $744.5 (a)	2,988.10				2,619.60
Total assets	$	3,134.40			$	2,770.60
Current liabilities	$	358.5			$	141
Long-term debt	2,012.90				1,963.10
Other liabilities	218.1				212.4
Shareholders’ equity	544.9				454.1
Total liabilities and shareholders' equity	$	3,134.40			$	2,770.60
_________
(a) All operating assets were pledged as collateral for long-term debt obligations.
The following table shows contractual future lease receipts from noncancelable leases of the RRPF affiliates as of December 31, 2014 (in millions):
	Rolls-Royce				Third Parties				Total
2015	$	144.6			$	158.9			$	303.5
2016	129.3				141.8				271.1
2017	109.7				130				239.7
2018	102.4				115.7				218.1
2019	97.1				70.7				167.8
Thereafter	212.3				216.2				428.5
	$	795.4			$	833.3			$	1,628.70
The following table shows maturities of debt obligations of the RRPF affiliates as of December 31, 2014 (in millions):
2015	$	277
2016	323.3
2017	252.2
2018	106.9
2019	426
Thereafter	904.5
Total debt principal (1)	$	2,289.90
_________
(1) All debt obligations are nonrecourse to the shareholders.

Loans

Loans	12 Months Ended
	Dec. 31, 2014
Loans Receivable, Net [Abstract]
Loans	We had total loans outstanding of $97.3 million at December 31, 2014 and $122.7 million at December 31, 2013. No loans were impaired at December 31, 2014 or 2013. In January 2015, Ahaus Alstätter Eisenbahn Cargo AG (“AAE”) repaid its outstanding loan in the amount of of €68.2 million ($77.0 million), including €67.5 million ($76.2 million) of remaining principal and €0.7 million ($0.8 million) of accrued interest.
	The following table shows scheduled loan principal payments due by year at December 31, 2014 (in millions):
	2015	$	86.4
	2016	4.3
	2017	2
	2018	4.6
	2019	—
	Thereafter	—
		$	97.3
	The following table shows changes in the allowance for losses at December 31 (in millions):
		2014			2013
	Beginning balance	$	5.2		$	4.6
	Provision for losses	0.8			0.7
	Charges to allowance	(0.3		)	—
	Recoveries and other, including foreign exchange adjustments	—			(0.1		)
	Ending balance	$	5.7		$	5.2
	The allowance for losses is comprised of a general allowance for trade receivables and specific allowances for finance leases. As of December 31, 2014, the general allowance for trade receivables was $4.5 million, or 5.2% of rent and other receivables, compared to $4.0 million, or 4.9% of rent and other receivables, at December 31, 2013. At December 31, 2014, specific allowances of $1.2 million were comparable to prior year.

Variable_Interest_Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2014
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Variable Interest Entities	We determined that we are the primary beneficiary of one of our variable interest entities, a structured lease financing of a portfolio of railcars, because we have the power to direct its significant activities. As a result, we consolidate this variable interest entity. The risks associated with it are similar to those of our wholly owned railcar leasing activities.
	The following table shows the carrying amounts of assets and liabilities of the consolidated variable interest entity as of December 31 (in millions):
		2014		2013
	Operating assets, net of accumulated depreciation (1)	$	88.1	$	93
	Nonrecourse debt	15.9		25.4
	_________
	-1	All operating assets are pledged as collateral on the nonrecourse debt.
	We determined that we are not the primary beneficiary of our other variable interest entities, which are primarily investments in railcar and equipment leasing affiliates that were financed through a variety of equity investments and third party lending arrangements. We are not the primary beneficiary of these variable interest entities because we do not have the power to direct the activities that most significantly impact the entities’ economic performance. For investments in affiliates we determined were variable interest entities, we concluded that power was shared by the affiliate partners based on the terms of the relevant joint venture agreements, which require approval of all partners for significant decisions regarding the variable interest entity.
	The following table shows the carrying amounts and maximum exposure to loss for our unconsolidated variable interest entities as of December 31 (in millions):
		2014				2013
		Net Carrying Amount		Maximum Exposure to Loss		Net Carrying Amount		Maximum Exposure to Loss
	Investments in affiliates	$	143.9	$	143.9	$	125.5	$	125.5
	Other investment	0.4		0.4		0.6		0.6
	Total	$	144.3	$	144.3	$	126.1	$	126.1

Debt

Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt	Commercial Paper and Borrowings Under Bank Credit Facilities ($ in millions)
		31-Dec
		2014			2013
	Balance	$	72.1		$	23.6
	Weighted average interest rate	0.56		%	0.8		%
	Recourse and Nonrecourse Debt Obligations
	The following table shows the outstanding balances of our debt obligations and the applicable interest rates as of December 31 ($ in millions):
		Date of Issue		Final	Interest Rate			2014			2013
				Maturity
	Recourse Fixed Rate Debt
	Unsecured	4/14/05		4/15/15	5.7	%		$	100		$	100
	Unsecured	2/5/10		5/15/15	4.75	%		250			250
	Unsecured	12/22/05		12/22/15	5.75	%		70			85
	Unsecured	3/3/06		3/1/16	5.8	%		200			200
	Unsecured	11/19/10		7/15/16	3.5	%		250			250
	Unsecured	9/20/11		7/15/16	3.5	%		100			100
	Unsecured	3/4/14		3/4/17	1.25	%		300			—
	Unsecured	2/6/08		2/15/18	6	%		200			200
	Unsecured	3/19/13		7/30/18	2.38	%		250			250
	Unsecured (1)	12/27/10		10/31/18	3.84	%		15.7			22
	Unsecured (1)	11/29/10		11/30/18	3.7	%		12.1			17.2
	Unsecured	11/19/13		3/15/19	2.5	%		300			300
	Unsecured	3/4/14		7/30/19	2.5	%		250			—
	Unsecured	10/31/14		3/30/20	2.6	%		250			—
	Unsecured	5/27/11		6/1/21	4.85	%		250			250
	Unsecured	9/20/11		6/1/21	4.85	%		50			50
	Unsecured	6/11/12		6/15/22	4.75	%		250			250
	Unsecured	3/19/13		3/30/23	3.9	%		250			250
	Unsecured	3/4/14		3/15/44	5.2	%		300			—
	Unsecured	4/30/09		5/15/14	8.75	%		—			300
	Total recourse fixed rate debt							$	3,647.80		$	2,874.20
	Recourse Floating Rate Debt
	Unsecured	12/15/10		10/31/15	1.47	%		$	24.8		$	36.4
	Unsecured (1)	12/6/11		8/31/16	1.57	%		15.3			22.1
	Unsecured (1)	9/2/11		8/31/16	1.13	%		8			11.5
	Unsecured (1)	3/29/06		9/30/16	2.08	%		18.9			32.2
	Unsecured (1)	6/29/07		9/30/16	2.03	%		8.5			14.4
	Unsecured (1)	12/18/07		10/31/16	1.98	%		12.7			21.6
	Unsecured	12/21/12		12/21/17	1.39	%		100			100
	Unsecured	1/22/13		12/21/17	1.39	%		10			70
	Unsecured (1)	8/31/12		12/31/19	2.33	%		60.5			68.7
		Date of Issue		Final	Interest Rate			2014			2013
				Maturity
	Unsecured (1)	6/27/13		12/31/20	1.87	%		121			137.5
	Unsecured (1)	10/30/13		12/31/20	1.91	%		30.2			34.4
	Unsecured (1)	5/5/14		12/31/20	1.99	%		30.2			—
	Unsecured	8/28/14		8/28/24	1.54	%		100			—
	Unsecured	3/1/10		2/28/15	1.83	%		—			13.7
	Unsecured	12/12/11		6/12/17	1.63	%		—			103.5
	Unsecured	8/12/13		6/12/17	1.63	%		—			71.1
	Unsecured	1/12/12		6/12/17	1.63	%		—			31.5
	Unsecured	2/21/13		12/21/17	1.81	%		—			35
	Secured	12/19/11		12/19/20	2.1	%		—			91.1
	Total recourse floating rate debt							$	540.1		$	894.7
	Nonrecourse Fixed Rate Debt
	Secured (1)	9/30/97		9/20/16	6.69	%		$	15.9		$	25.4
	Total nonrecourse fixed rate debt							$	15.9		$	25.4
	Nonrecourse Floating Rate Debt
	Secured	Various		5/8/14	1.4	%		$	—		$	47.7
	Total nonrecourse floating rate debt							$	—		$	47.7
	Total debt principal							$	4,203.80		$	3,842.00
	Debt discount, net							(8.6		)	(8.9		)
	Debt adjustment for fair value hedges							0.6			5.4
	Total Debt							$	4,195.80		$	3,838.50
__________
(1) Amount shown includes scheduled principal payments prior to the final maturity.
The following table shows the scheduled principal payments of our debt obligations as of December 31, 2014 (in millions):
2015	$	529.2
2016	639.2
2017	455.4
2018	507.5
2019	592.3
Thereafter	1,480.20
Total debt principal	$	4,203.80
At December 31, 2014 we had $95.9 million of our operating assets pledged as collateral for notes or other obligations.
Shelf Registration Statement
During the third quarter of 2013, we filed an updated shelf registration statement that enables us to issue debt securities and pass-through certificates. The registration statement is effective for three years and does not limit the amount of debt securities and pass-through certificates we can issue.
Credit Lines and Facilities
In 2013, we entered into a new $575 million 5-year unsecured revolving credit facility in the US. In 2014, we exercised an option to extend the maturity date of our revolving credit facility by one year, to April 30, 2019. At December 31, 2014, available capacity under the credit facility was $506.0 million, reflecting $69.0 million of outstanding commercial paper, which is backed by the facility.
Annual commitment fees for the revolving credit facility are based on a percentage of the commitment and were $0.8 million for 2014, $1.0 million for 2013, and $1.2 million for 2012.
Restrictive Covenants
Our $575 million revolving credit facility contains various restrictive covenants, including requirements to maintain a fixed charge coverage ratio and an asset coverage test. Our ratio of earnings to fixed charges, as defined in this facility, was 2.5 for the period ended December 31, 2014, which is in excess of the minimum covenant ratio of 1.2. At December 31, 2014, we were in compliance with all covenants and conditions of the facility. Some of our bank term loans have the same financial covenants as the facility.
As of December 31, 2014, the indentures for our public debt also contain various restrictive covenants, including limitation on liens provisions that limit the amount of additional secured indebtedness that we may incur to $1,283.1 million. Additionally, certain exceptions to the covenants permit us to incur an unlimited amount of purchase money and nonrecourse indebtedness. At December 31, 2014, we were in compliance with all covenants and conditions of the indentures.
The loan agreements for our European rail subsidiaries ( "GATX Rail Europe" or "GRE") also contain restrictive covenants, including leverage and cash flow covenants specific to those subsidiaries, restrictions on making loans, and limitations on the ability of those subsidiaries to repay loans or to distribute capital to certain related parties (including GATX, the US parent company). These covenants effectively limit GRE's ability to transfer funds to us. At December 31, 2014, the maximum amount that GRE could transfer to us without violating its covenants was $111.3 million, therefore implying the loan covenants restrict $391.2 million of subsidiary net assets. At December 31, 2014, GRE was in compliance with all covenants and conditions of these loan agreements.
Another subsidiary’s financing that is guaranteed by us contains various restrictive covenants, including covenants that require us to maintain a defined net worth and a fixed charge coverage ratio. This fixed charge coverage ratio covenant is less restrictive than the covenant in our revolving credit facility.
We do not anticipate any covenant violations nor do we anticipate that any of these covenants will restrict our operations or our ability to obtain additional financing.

Fair_Value_Disclosure

Fair Value Disclosure	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Disclosure	Fair Value Disclosure
	The following tables show our assets and liabilities that are measured at fair value on a recurring basis (in millions):
	Assets	Total			Quoted Prices in Active Markets for Identical Assets			Significant Observable Inputs			Significant Unobservable Inputs
		December 31,			(Level 1)			(Level 2)			(Level 3)
		2014
	Interest rate derivatives (1)	$	1.8		$	—		$	1.8		$	—
	Foreign exchange rate derivatives (2)	9.7			—			9.7			—
	Available-for-sale equity securities	4.4			4.4			—			—
	Liabilities
	Interest rate derivatives (1)	5.9			—			5.9			—
	Foreign exchange rate derivatives (2)	1.6			—			1.6			—
	Assets	Total			Quoted Prices in Active Markets for Identical Assets			Significant Observable Inputs			Significant Unobservable Inputs
		December 31,			(Level 1)			(Level 2)			(Level 3)
		2013
	Interest rate derivatives (1)	$	6		$	—		$	6		$	—
	Available-for-sale equity securities	4.7			4.7			—			—
	Liabilities
	Interest rate derivatives (1)	0.8			—			0.8			—
	Interest rate derivatives (2)	0.2			—			0.2			—
	Foreign exchange rate derivatives (2)	2.6			—			2.6			—
	_________
	-1	Designated as hedges.
	-2	Not designated as hedges.
	We base our valuations of available-for-sale equity securities on their quoted prices on an active exchange. We value derivatives using a pricing model with inputs (such as yield curves and credit spreads) that are observable in the market or that can be derived principally from observable market data.
	The following table shows disclosures related to our non-recurring Level 3 fair value measurements (in millions):
		Fair Value			Impairment Losses
		of Assets
	2014
	Operating assets (1)	$	2.5		$	0.7
	2013
	Operating assets (1)	9.6			2.5
	2012
	Investment in affiliated companies (2)	32.9			14.8
	Operating assets (1)	0.7			0.7
	_________
	-1	We based the fair values for operating assets on the expected future proceeds we expect to receive from the assets, including proceeds from their disposition. Impairment losses on operating assets generally related to certain railcars, vessels, and other long-lived assets.
	-2	Impairment losses related to our Enerven affiliate. The fair value of the Enerven affiliate was primarily based on proceeds expected to be received upon the sale of all assets and completion of liquidation proceedings.
	Derivative instruments
	Fair Value Hedges
	We use interest rate swaps to manage the fixed-to-floating rate mix of our debt obligations by converting the fixed rate debt to floating rate debt. For fair value hedges, we recognize changes in fair value of both the derivative and the hedged item as interest expense. We had eight instruments outstanding with an aggregate notional amount of $600.0 million as of December 31, 2014 and three instrument outstanding with an aggregate notional amount of $200.0 million as of December 31, 2013. These derivatives have maturities ranging from 2015 to 2020.
	Cash Flow Hedges
	We use interest rate swaps to convert floating rate debt to fixed rate debt. We use Treasury rate locks to hedge our exposure to interest rate risk on anticipated transactions. We also use currency swaps to hedge our exposure to fluctuations in the exchange rates of the foreign currencies in which we conduct business. We had seven instruments outstanding with an aggregate notional amount of $281.5 million as of December 31, 2014 and six instruments outstanding with an aggregate notional amount of $163.6 million as of December 31, 2013. These derivatives had maturities ranging from 2015 to 2020. Within the next 12 months, we expect to reclassify $6.0 million ($3.8 million after-tax) of net losses on previously terminated derivatives from accumulated other comprehensive income (loss). We reclassify these amounts when interest and operating lease expense on the related hedged transactions affect earnings.
	Non-designated Derivatives
	We do not hold derivative financial instruments for purposes other than hedging, although certain of our derivatives are not designated as accounting hedges. We recognize changes in the fair value of these derivatives in other (income) expense immediately.
	Some of our derivative instruments contain credit risk provisions that could require us to make immediate payment on net liability positions in the event that we default on certain outstanding debt obligations. The aggregate fair value of our derivative instruments with credit risk related contingent features that are in a liability position as of December 31, 2014 was $5.9 million. We are not required to post any collateral on our derivative instruments and do not expect the credit risk provisions to be triggered.
	In the event that a counterparty fails to meet the terms of an interest rate swap agreement or a foreign exchange contract, our exposure is limited to the fair value of the swap, if in our favor. We manage the credit risk of counterparties by transacting with institutions that we consider financially sound and by avoiding concentrations of risk with a single counterparty. We believe that the risk of non-performance by any of our counterparties is remote.
	The following table shows the impacts of our derivative instruments on our statement of comprehensive income for the years ended December 31 (in millions):
	Derivative Designation		Location of Loss (Gain) Recognized	2014			2013			2012
	Fair value hedges (1)		Interest expense	$	4.7		$	4.9		$	5
	Cash flow hedges		Other comprehensive loss (effective portion)	5.1			(0.7		)	0.2
	Cash flow hedges		Interest expense (effective portion reclassified from accumulated other comprehensive loss)	4.9			5.1			4.2
	Cash flow hedges		Operating lease expense (effective portion reclassified from accumulated other comprehensive loss)	3.2			1.5			1.4
	Cash flow hedges		Other (income) expense (effective portion reclassified from accumulated other comprehensive loss)	(2.1		)	—			—
	Cash flow hedges		Other (income) expense (ineffective portion)	—			—			(0.1		)
	Non-designated (2)		Other (income) expense	(11.4		)	(0.6		)	5
	_________
	-1	The fair value adjustments related to the underlying debt equally offset the amounts recognized in interest expense.
	-2	For 2014, includes $10.4 million of gains on foreign currency derivatives which substantially offset losses from foreign currency remeasurement adjustments on the AAE loan, also recognized in other income.
	Other Financial Instruments
	The carrying amounts of cash and cash equivalents, restricted cash, rent and other receivables, accounts payable, and commercial paper and bank credit facilities approximate fair value due to the short maturity of those instruments. We base the fair values of investment funds, which are accounted for under the cost method, on the best information available, which may include quoted investment fund values. We estimate the fair values of loans and fixed and floating rate debt using discounted cash flow analyses that are based on interest rates currently offered for loans with similar terms to borrowers of similar credit quality. The inputs we use to estimate each of these values are classified in Level 2 of the fair value hierarchy because they are directly or indirectly observable inputs.
	The following table shows the carrying amounts and fair values of our other financial instruments as of December 31 (in millions):
		2014			2014			2013			2013
		Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value
Assets
Investment funds	$	1.5		$	2.4		$	1.7		$	4
Loans	97.3			97.4			122.7			121.5
Liabilities
Recourse fixed rate debt	$	3,639.90		$	3,775.00		$	2,871.20		$	2,994.00
Recourse floating rate debt	540			540			894.7			906.2
Nonrecourse debt	15.9			16.6			72.6			74.7

Pension_and_Other_PostRetireme

Pension and Other Post-Retirement Benefits	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Pension and Other Post-Retirement Benefits	We maintain both funded and unfunded noncontributory defined benefit pension plans covering our domestic employees and the employees of our subsidiaries. We also have a funded noncontributory defined benefit pension plan related to a former business in the United Kingdom that has no active employees. The plans base benefits payable on years of service and/or final average salary. We base our funding policies for the pension plans on actuarially determined cost methods allowable under IRS regulations and statutory requirements in the UK.
	In addition to the pension plans, we have other post-retirement plans that provide health care, life insurance, and other benefits for certain retired domestic employees who meet established criteria. Most domestic employees that retire with immediate benefits under our pension plan are eligible for health care and life insurance benefits. The other post-retirement plans are either contributory or noncontributory, depending on various factors.
	We use a December 31 measurement date for all of our plans. The following tables show pension obligations, plan assets, and other post-retirement obligations as of December 31 (in millions):
		2014 Pension				2013 Pension				2014 Retiree			2013 Retiree
		Benefits				Benefits				Health			Health
										and Life			and Life
	Change in Benefit Obligation
	Benefit obligation at beginning of year	$	442.7			$	473.8			$	40.4		$	48.1
	Service cost	5.9				6.7				0.1			0.2
	Interest cost	20.7				18.4				1.6			1.6
	Actuarial loss (gain)	67				(26.8		)		2.6			(6.2		)
	Benefits paid	(31.2		)		(30.3		)		(3.9		)	(3.3		)
	Effect of foreign exchange rate changes	(2.4		)		0.9				—			—
	Benefit obligation at end of year	$	502.7			$	442.7			$	40.8		$	40.4
	Change in Fair Value of Plan Assets
	Plan assets at beginning of year	447.8				409.1				—			—
	Actual return on plan assets	40.3				65.9				—			—
	Effect of exchange rate changes	(2.4		)		0.7				—			—
	Company contributions	2.4				2.4				3.9			3.3
	Benefits paid	(31.2		)		(30.3		)		(3.9		)	(3.3		)
	Plan assets at end of year	$	456.9			$	447.8			$	—		$	—
	Funded Status at end of year	$	(45.8	)		$	5.1			$	(40.8	)	$	(40.4	)
	Amount Recognized
	Other liabilities (assets), net	$	(45.8	)		$	5.1			$	(40.8	)	$	(40.4	)
	Accumulative other comprehensive loss:
	Net actuarial loss	170.9				127.6				3.3			0.6
	Prior service (credit) cost	(2.1		)		(3.1		)		0.4			0.4
	Accumulated other comprehensive loss	168.8				124.5				3.7			1
	Total recognized	$	123.2			$	129.6			$	(37.1	)	$	(39.4	)
	After-tax amount recognized in accumulated other comprehensive loss	$	105.4			$	77.6			$	2.3		$	0.6
	The aggregate accumulated benefit obligation for the defined benefit pension plans was $475.8 million at December 31, 2014 and $426.3 million at December 31, 2013.
	The following table shows our pension plans that have a projected benefit obligation in excess of plan assets as of December 31 (in millions):
		2014				2013
	Projected benefit obligations	$	502.7			$	67.8
	Fair value of plan assets	456.9				40
	The following table shows our pension plans that have an accumulated benefit obligation in excess of plan assets as of December 31 (in millions):
		2014				2013
	Accumulated benefit obligations	$	170.6			$	66.4
	Fair value of plan assets	140.5				40
	The following table shows the components of net periodic cost (benefit) for the year ended December 31 (in millions):
		2014				2013				2012			2014			2013			2012
		Pension				Pension				Pension			Retiree Health and Life			Retiree Health and Life			Retiree Health and Life
		Benefits				Benefits				Benefits
	Service cost	$	5.9			$	6.7			$	5.7		$	0.1		$	0.2		$	0.2
	Interest cost	20.7				18.4				19.7			1.6			1.6			2
	Expected return on plan assets	(28.4		)		(27.5		)		(29.6		)	—			—			—
	Amortization of:
	Unrecognized prior service credit	(1.0		)		(1.0		)		(1.0		)	(0.1		)	(0.1		)	(0.1		)
	Unrecognized net actuarial loss (gain)	11.3				14.9				9.9			(0.1		)	—			(0.1		)
	Net periodic cost	$	8.5			$	11.5			$	4.7		$	1.5		$	1.7		$	2
	We amortize the unrecognized prior service credit using a straight-line method over the average remaining service period of the employees we expect to receive benefits under the plan. We amortize the unrecognized net actuarial loss (gain), which is subject to certain averaging conventions, over the average remaining service period of active employees.
	The following table shows the amounts we expect to recognize as components of net periodic cost in 2015 from amounts recorded in accumulated comprehensive loss (gain) as of December 31, 2014 (in millions):
		2015
		Pension Benefits				Retiree Health and Life
	Unrecognized net actuarial loss	$	14.1			$	0.1
	Unrecognized prior service credit (cost)	(1.0		)		0.1
	We use the following assumptions to measure the benefit obligation, compute the expected long-term return on assets, and measure the periodic cost for our defined benefit pension plans and other post-retirement benefit plans for the years ended December 31:
		2014			2013
	Domestic defined benefit pension plans
	Benefit Obligation at December 31:
	Discount rate — salaried funded and unfunded plans	4.05	%		4.8	%
	Discount rate — hourly funded plan	4.1	%		4.9	%
	Rate of compensation increases — salaried funded and unfunded plans	2.5	%		3	%
	Rate of compensation increases — hourly funded plans	N/A			N/A
Net Periodic Cost (Benefit) for the years ended December 31:
Discount rate — salaried funded and unfunded plans	4.8	%		3.95	%
Discount rate — hourly funded plan	4.9	%		4.05	%
Expected return on plan assets — salaried funded plan	7.6	%		7.75	%
Expected return on plan assets — hourly funded plan	6.9	%		6.8	%
Rate of compensation increases — salaried funded and unfunded plans	3	%		3	%
Rate of compensation increases — hourly funded plan	N/A			N/A
Foreign defined benefit pension plan
Benefit Obligation at December 31:
Discount rate	3.2	%		4.4	%
Rate of pension-in-payment increases	2.9	%		3.4	%
Net Periodic Cost (Benefit) for the years ended December 31:
Discount rate	4.4	%		4.25	%
Expected return on plan assets	5.4	%		5.34	%
Rate of pension-in-payment increases	3.4	%		3	%
Other post-retirement benefit plans
Benefit Obligation at December 31:
Discount rate - salaried health	3.65	%		4.2	%
Discount rate - hourly health	3.85	%		4.6	%
Discount rate - salaried life insurance	4	%		4.75	%
Discount rate - hourly life insurance	3.7	%		4.4	%
Rate of compensation increases	N/A			N/A
Net Periodic Cost (Benefit) for the years ended December 31:
Discount rate - salaried health	4.2	%		3.65	%
Discount rate - hourly health	4.6	%		3.6	%
Discount rate - salaried life insurance	4.75	%		3.9	%
Discount rate - hourly life insurance	4.4	%		3.45	%
Rate of compensation increases	N/A			N/A
We calculate the present value of expected future pension and post-retirement cash flows as of the measurement date using a discount rate. We base the discount rate on yields for high-quality, long-term bonds with durations similar to that of our projected benefit obligation. We base the expected return on our plan assets on current and expected asset allocations, as well as historical and expected returns on various categories of plan assets. We routinely review our historical returns along with current market conditions to ensure our expected return assumption is reasonable and appropriate.
	2014			2013
Assumed Health Care Cost Trend Rates at December 31
Health care cost trend assumed for next year
Medical claims	7.5	%		8	%
Prescription drugs claims	7	%		7	%
Rate to which the cost trend is expected to decline (the ultimate trend rate)
Medical claims	5	%		5	%
Prescription drugs claims	5	%		5	%
Year that rate reaches the ultimate trend rate
Medical claims	2023			2020
Prescription drugs claims	2023			2020
The health care cost trend, which is based on projected growth rates for medical and prescription drug claims, has a significant effect on our other post-retirement benefit costs and obligations. The following table shows the effects of a one percentage point change in the health care cost trend rate on service and interest costs for the year ended December 31, 2014 and the post-retirement benefit obligation as of December 31, 2014 (in millions) :
	One Percentage Point				One Percentage Point
	Increase				Decrease
Effect on total of service and interest cost	$	0.1			$	(0.1	)
Effect on post-retirement benefit obligation	2.6				(2.3		)
Our investment policies require that asset allocations of domestic and foreign funded pension plans be maintained at certain targets. The following table shows our weighted-average asset allocations of our domestic funded pension plans at December 31, 2014 and 2013, and current target asset allocation for 2015, by asset category:
				Plan Assets at
				31-Dec
	Target			2014			2013
Asset Category
Equity securities	52	%		51.7	%		66.7	%
Debt securities	44	%		43.9	%		27.8	%
Real estate	4	%		4.3	%		5.4	%
Cash	—	%		0.1	%		0.1	%
	100	%		100	%		100	%
The following table shows the weighted-average asset allocations of our foreign funded pension plan at December 31, 2014 and 2013, and current target asset allocation for 2015, by asset category:
				Plan Assets at
				31-Dec
	Target			2014			2013
Asset Category
Equity securities	36.8	%		37.7	%		38.5	%
Debt securities	63.2	%		62.3	%		61.5	%
	100	%		100	%		100	%
The following tables set forth the fair value of our pension plan assets as of December 31 (in millions):
	Total				Quoted Prices in Active Markets for Identical Assets				Significant Observable Inputs			Significant Unobservable Inputs (Level 3)
	December 31,				(Level 1)				(Level 2)
	2014
Assets
Short-term investment funds	$	0.9			$	0.9			$	—		$	—
Common stock												—
US equities	13.3				13.3				—			—
International equities	1.6				1.6				—			—
Common stock collective funds	215.2				—				215.2			—
Fixed income collective trust funds	208.1				—				208.1			—
Real estate collective trust funds	17.9				—				17.9			—
Total	$	457			$	15.8			$	441.2		$	—
	Total				Quoted Prices in Active Markets for Identical Assets				Significant Observable Inputs			Significant Unobservable Inputs (Level 3)
	December 31,				(Level 1)				(Level 2)
	2013
Assets
Short-term investment funds	$	1.3			$	1.3			$	—		$	—
Common stock												—
US equities	21.4				21.4				—			—
International equities	2.4				2.4				—			—
Common stock collective funds	263				—				263			—
Fixed income collective trust funds	138				—				138			—
Real estate collective trust funds	21.7				—				21.7			—
Total	$	447.8			$	25.1			$	422.7		$	—
The following is a description of the valuation techniques and inputs used as of December 31, 2014 and 2013:
Short-term investment funds
We value short-term investment funds based on the closing net asset values quoted by the funds. The net asset values are the unitized fair values of the underlying securities held by the trusts, which are traded in an active market. Short-term investment funds are highly liquid investments in obligations of the US Government or its agencies or instrumentalities, and the related money market instruments. The short-term investment funds have no unfunded commitments, restrictions on redemption frequency, or advance notice periods required for redemption.
Common stock
We value common stock traded in an active market at the last reported sales price on the last business day of the plan year.
Common stock and fixed income collective trust funds
We value common stock and fixed income collective trust funds based on the closing net asset values quoted by the funds. The net asset values are the unitized fair values of the underlying securities held by the trusts, which are traded in an active market. None of the collective trusts have unfunded commitments, restrictions on redemption frequency, or advance notice periods required for redemption. The investment objective of each of the common stock funds is long-term total return through capital appreciation and current income. The fixed income funds are each designed to deliver safety and stability by preserving principal and accumulated earnings.
Real estate collective trust funds
We value real estate collective trust funds based on the net asset values provided by the funds' administrators, which are the unitized fair values of the underlying US commercial real estate investments held by the funds. An independent appraisal determines the fair values of the real estate properties. Redemptions from the real estate funds are available with either 45 or 60 day notice prior to the end of a quarter. A lack of liquidity in the funds may limit or delay redemptions. The investment objective of the real estate funds, which are diversified by location and property type, is long-term return through property appreciation, current income, and timely sales.
The primary investing objective of the pension plans is to provide benefits to plan participants and their beneficiaries. To achieve this goal, we invest in a diversified portfolio of equities, debt, and real estate investments to maximize return and to keep long-term investment risk at a reasonable level. Equity investments are diversified across US and non-US stocks, growth and value stocks, and small cap and large cap stocks. Debt securities are predominately investments in long-term, investment-grade corporate bonds. Real estate investments include investments in funds that are diversified by location and property type.
On a timely basis, but not less than twice a year, we formally review pension plan investments to ensure we adhere to investment guidelines and our stated investment approach. Our review also evaluates the reasonableness of our investment decisions and risk positions. We compare our investments' performance to indices and peers to determine if investment performance has been acceptable.
In 2015, we expect to contribute approximately $6.0 million to our pension and other post-retirement benefit plans. Additional contributions to the domestic funded pension plans will depend on investment returns on plan assets and actuarial experience.
The following table shows benefit payments, which reflect expected future service, as appropriate, we expect the plan to pay (in millions):
	Funded Plans				Unfunded Plans				Retiree Health and Life
2015	$	28.2			$	2			$	3.5
2016	28.3				2.2				3.4
2017	28.7				2.3				3.3
2018	29.2				2.3				3.2
2019	29.6				2.8				3.1
Years 2020-2024	152.2				15.3				14
	$	296.2			$	26.9			$	30.5
In addition to our defined benefit plans, we have two 401(k) retirement plans available to substantially all salaried employees and certain other employee groups. We may contribute to the plans as specified by their respective terms and as our board of directors determines. Contributions to our 401(k) retirement plans were $1.8 million for 2014, $1.6 million for 2013, and $1.6 million for 2012.
Multiemployer Plans
Most of the shipboard personnel at ASC participate in various multiemployer benefit plans that provide pension, health care, and post-retirement and other benefits to active and retired employees. Unlike single employer plans, we do not recognize plan assets or obligations for multiemployer plans on our balance sheet. Rather, we recognize our contributions to the plans as marine operating expenses. The amounts we contribute are based on the number of crew hours worked, which depends on the number of vessels deployed and aggregate operating days in a particular year. The risks of participating in these multiemployer plans are different from single employer plans in the following aspects:
•	Assets contributed by one employer may be used to provide benefits to employees of other participating employers;
•	If a participating employer fails to make its required contributions, any unfunded obligations of the plan may be the responsibility of the remaining participating employers; and
•	If an employer chooses to stop participating in a multiemployer plan, the plan may require the withdrawing company to make additional contributions.
The following table shows our contributions to multiemployer benefit plans for the years indicated (in millions):
Multiemployer Plans		EIN and Pension Plan Number		Pension Protection Act Zone Status		GATX Contributions										Collective Bargaining Agreement Expiration Date
						2014				2013			2012
American Maritime Officers Pension Plan (1)		13-1969709-001		Endangered-Yellow		$	1.5			$	1.4		$	1.5		January 15, 2017
Other multiemployer post-retirement plans						7				6.7			6.6
Total						$	8.5			$	8.1		$	8.1
__________________
(1)Our contributions represented more than 5% of the total contributions to the plan during each year and no surcharge was imposed for any year. The actuary for the American Maritime Officers Pension Plan certified that the plan is in endangered status (i.e. “yellow zone” as defined by the Pension Protection Act of 2006) for the plan year beginning October 1, 2013, because it has funding or liquidity problems, or both. A rehabilitation plan, as defined by the Employee Retirement Security Act of 1974, was instituted under which certain adjustable benefits were reduced or eliminated, and we are required to contribute at a negotiated rate per day worked by each employee.

ShareBased_Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation
	We provide equity awards to our employees under the GATX Corporation 2012 Incentive Award Plan, including grants of stock appreciation rights, restricted stock units, performance shares and phantom stock awards. As of December 31, 2014, 3.5 million shares were authorized under the 2012 Plan and 2.4 million shares were available for future issuance. We recognize compensation expense for our equity awards in selling, general and administrative expenses over the service period of each award. Share-based compensation expense was $14.0 million for 2014, $13.1 million for 2013, and $12.2 million for 2012, and the related tax benefits were $5.3 million for 2014, $4.9 million for 2013, and $4.6 million for 2012.
	Stock Options and Stock Appreciation Rights
	Stock options and stock appreciation rights entitle the holder to purchase shares of common stock for periods up to seven years from the grant date. Stock appreciation rights entitle the holder to receive the difference between the market price of our common stock at the time of exercise and the exercise price, either in shares of common stock, cash, or a combination thereof, at our discretion. Stock options entitle the holder to purchase shares of our common stock at a specified exercise price. Since 2006, only stock-settled stock appreciation rights have been awarded. The dividends that accrue on all stock options and stock appreciation rights are paid upon vesting and continue to be paid until the stock options or stock appreciation rights are exercised, canceled, or expire. The exercise price for stock options and stock appreciation rights is equal to the average of the high and low trading prices of our common stock on the date of grant. We recognize compensation expense on a straight-line basis over the vesting period of the award, which is generally three years.
	The estimated fair value of a stock appreciation right is the sum of the value we derive using the Black-Scholes option pricing model and the present value of dividends we expect to pay over the expected term of the stock appreciation right. The Black-Scholes valuation incorporates various assumptions, including expected term, expected volatility, and risk free interest rates. We base the expected term on historical exercise patterns and post-vesting terminations, and we base the expected volatility on the historical volatility of our stock price over a period equal to the expected term. We use risk-free interest rates that are based on the implied yield on recently-issued US Treasury zero-coupon bonds with a term comparable to the expected term.
	The following table shows the weighted average fair value for our stock appreciation rights and the assumptions we used to estimate fair value:
		2014				2013			2012
	Weighted average estimated fair value	$	18.12			$	18.89		$	18.48
	Quarterly dividend rate	$	0.33			$	0.3		$	0.29
	Expected term of stock appreciation rights, in years	4.4				4.7			4.7
	Risk-free interest rate	1.3		%		0.7		%	1		%
	Dividend yield	2.3		%		2.6		%	2.7		%
	Expected stock price volatility	30.3		%		42.4		%	43.3		%
	Present value of dividends	$	5.76			$	5.6		$	5.37
	The following table shows information about outstanding stock options and stock appreciation rights for the year ended December 31, 2014:
		Number of Stock Options and Stock Appreciation Rights		Weighted Average Exercise Price
		(in thousands)
	Outstanding at beginning of the year	1,694		$	36.03
	Granted	297		58.5
	Exercised	-467		37.71
	Forfeited/Cancelled	-33		50.71
	Expired	-1		41.02
	Outstanding at end of the year	1,490		39.65
	Vested and exercisable at end of the year	919		32.08
	The following table shows the aggregate intrinsic value of stock options and stock appreciation rights exercised in 2014, 2013, and 2012, and the weighted average remaining contractual term and aggregate intrinsic value of stock appreciation rights outstanding and vested as of December 31, 2014:
	Stock Options and Stock Appreciation Rights	Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
		(Years)		(in millions)
	Exercised in 2012			$	4.9
	Exercised in 2013			6.9
	Exercised in 2014			11.8
	Outstanding at December 31, 2014 (a)	3.7		27.5
	Vested and exercisable at December 31, 2014	2.6		23.8
	__________________
	(a) As of December 31, 2014, there are no remaining stock options outstanding.
	As of December 31, 2013, all stock options were either exercised or called. Therefore, no cash was received from employees for exercises of stock options during the year ended December 31, 2014. The total cash we received from employees for exercises of stock options during the years ended December 31, 2013 and December 31, 2012 was $1.2 million and $5.6 million. As of December 31, 2014, we had $14.1 million of unrecognized compensation expense related to nonvested stock appreciation rights, which we expect to recognize over a weighted average period of 1.7 years.
	Restricted Stock Units and Performance Shares
	Restricted stock units entitle the recipient to receive a specified number of restricted shares of common stock upon vesting. Restricted stock units do not carry voting rights and are not transferable prior to the expiration of a specified restriction period, which is generally three years, as determined by the Compensation Committee of the Board of Directors ("Compensation Committee"). We accrue dividends on all restricted stock units and pay those dividends when the awards vest. We recognize compensation expense for these awards over the applicable vesting period.
	Performance shares are restricted shares that we grant to key employees for achieving certain strategic objectives. The shares convert to common stock at the end of a specified performance period if predetermined performance goals are achieved, as determined by the Compensation Committee. We estimate the number of shares we expect will vest as a result of actual performance against the performance criteria at the time of grant to determine total compensation expense to be recognized. We reevaluate the estimate annually and adjust total compensation expense for any changes to the estimate of the number of shares we expect to vest. We recognize compensation expense for these awards over the applicable vesting period, which is generally three years. The performance shares granted in 2014 include an option to settle shares earned in cash upon vesting.
	We value our restricted stock units and performance share awards using the average of the high and low values of our common stock on the grant date of the awards. As of December 31, 2014, there was $7.9 million of unrecognized compensation expense related to these awards, which we expect to be recognized over a weighted average period of 1.8 years.
	The following table shows information about restricted stock units and performance shares for the year ended December 31, 2014:
		Number of Share Units Outstanding			Weighted Average Grant-Date Fair Value
	Restricted Stock Units:
	Nonvested at beginning of the year	200,050			$	41.17
	Granted	56,020			58.66
	Vested	(70,986	)		34.77
	Forfeited	(7,874	)		49.42
	Nonvested at end of the year	177,210			48.9
	Performance Shares:
	Nonvested at beginning of the year	160,332			$	44.48
	Granted	62,670			53.63
	Net increase due to estimated performance	67,392			47.49
	Vested	(92,958	)		44.02
	Forfeited	(22,367	)		46.57
	Nonvested at end of the year	175,069			48.95
	The total fair value of restricted stock units and performance shares that vested during the year was $6.6 million in 2014, $7.5 million in 2013, and $5.6 million in 2012.
	Phantom Stock Awards
	We grant phantom stock awards to non-employee directors as a component of their compensation for service on our board of directors. In accordance with the terms of the phantom stock awards, each director is credited with a quantity of units that equate to, but are not, common shares. Phantom stock awards are dividend participating, and all dividends are reinvested in additional phantom shares at the average of the high and low trading prices of our stock on the dividend payment date. At the expiration of each director’s service on the board of directors, or in accordance with his or her deferral election, whole units of phantom stock will be settled with shares of common stock and fractional units will be paid in cash. In 2014, we granted 17,473 units of phantom stock and there were 147,962 units outstanding as of December 31, 2014.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Deferred income taxes are the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. We have not recognized deferred US income taxes on the undistributed earnings of foreign subsidiaries and affiliates that we intend to permanently reinvest in foreign operations. The cumulative amount of such earnings was $727.7 million at December 31, 2014. The ultimate tax cost of repatriating these earnings depends on tax laws in effect and other circumstances at the time of distribution.
	The following table shows the significant components of our deferred tax liabilities and assets as of December 31 (in millions):
		2014			2013
	Deferred Tax Liabilities
	Book/tax basis difference due to depreciation	$	963.8		$	852
	Investments in affiliated companies	99.7			93.7
	Lease accounting	10.5			24.4
	Other	0.1			—
	Total deferred tax liabilities	1,074.10			970.1
	Deferred Tax Assets
	Federal net operating loss	41.8			8.9
	Alternative minimum tax credit	9.2			8.4
	Foreign tax credit	3.6			3.6
	Valuation allowance on foreign tax credit	(3.6		)	(3.6		)
	State net operating loss	28.7			27.1
	Valuation allowance on state net operating loss	(11.3		)	(11.2		)
	Foreign net operating loss	5.8			8.5
	Valuation allowance on foreign net operating loss	(0.2		)	(0.2		)
	Accruals not currently deductible for tax purposes	18.7			14.1
	Allowance for losses	1.7			2.2
	Pension and post-retirement benefits	32.6			13.3
	Other	9.8			7.6
	Total deferred tax assets	136.8			78.7
	Net deferred tax liabilities	937.3			$	891.4
	At December 31, 2014, we have a US federal tax net operating loss carryforward of $119.3 million that will expire in 2033. We also have an alternative minimum tax credit of $9.2 million that has an unlimited carryforward period.
	At December 31, 2014, we have foreign tax credits of $3.6 million that are scheduled to expire beginning in 2016. We have recorded a $3.6 million valuation allowance related to these credits, as we believe it is more likely than not that we will be unable to utilize them. We also have state net operating losses of $28.7 million, net of federal benefits that are scheduled to expire at various times beginning in 2015. We have recorded an $11.3 million valuation allowance related to state net operating losses, as we believe it is more likely than not that we will be unable to use all of these losses. Additionally, we have foreign net operating losses, net of valuation allowances, of $5.6 million which have unlimited carryforward periods. Our use of future tax credits and net operating losses depends on a number of variables, including the amount of taxable income, foreign source income attributes, and state apportionment factors.
	The following table shows a reconciliation of the beginning and ending amount of our gross liability for unrecognized tax benefits (in millions)
		2014			2013
	Beginning balance	$	5.7		$	4.7
	Reductions due to settlement of tax audit issues	(0.4		)	—
	Additions to tax positions for prior years	0.3			1
	Ending balance	$	5.6		$	5.7
	At December 31, 2014, our gross liability for unrecognized tax benefits was $5.6 million, of which $3.6 million, if recognized, would favorably impact income tax expense. During the year ended December 31, 2014, we settled a tax audit recognizing a tax benefit of $0.4 million. Additionally, in 2014, we added a gross state tax liability of $0.3 million (net tax expense impact of $0.2 million). During the year ended December 31, 2013, we added a gross state tax liability of $1.0 million (net tax expense impact of $0.6 million). We recognize interest and penalties related to unrecognized tax benefits as income tax expense. We have not accrued any amounts for penalties. To the extent interest is not assessed or is otherwise reduced with respect to uncertain tax positions, we will record any required adjustment as a reduction of income tax expense.
	We file one consolidated federal income tax return with our domestic subsidiaries in the US jurisdiction, as well as tax returns in various state and foreign jurisdictions. As of December 31, 2014, all audits with respect to our federal tax returns for years prior to 2010 have been closed. However, GATX and our subsidiaries are undergoing audits in various state and foreign jurisdictions.
	The following table shows the components of income before income taxes, excluding affiliates, for the years ending December 31 (in millions):
		2014			2013			2012
	Domestic	$	137.9		$	66		$	80.5
	Foreign	93.3			93			63.3
		$	231.2		$	159		$	143.8
	The following table shows income taxes, excluding domestic and foreign joint ventures, for the years ending December 31 (in millions):
		2014			2013			2012
	Current
	Domestic:
	Federal	$	0.7		$	1.4		$	(8.8	)
	State and local	0.6			—			2.5
		1.3			1.4			(6.3		)
	Foreign	13			10.5			8
		14.3			11.9			1.7
	Deferred
	Domestic:
	Federal	45			36.6			16
	State and local	5.6			5.3			(3.1		)
		50.6			41.9			12.9
	Foreign	10.8			11.7			11.5
		61.4			53.6			24.4
	Income taxes	$	75.7		$	65.5		$	26.1
	The following table shows the differences between our effective income tax rate and the federal statutory income tax rate for the years ending December 31 (in millions):
		2014			2013			2012
	Income taxes at federal statutory rate	$	80.9		$	55.6		$	50.4
	Adjust for effect of:
	GATX income taxes on sale of AAE	—			23.2			—
	Foreign tax credits	—			(3.9		)	(13.7		)
	Foreign earnings taxed at lower rates	(8.5		)	(10.3		)	(4.1		)
	Tax effect of foreign dividends	—			—			6.3
Expiration of the applicable statute of limitations	—			—			(15.5		)
Corporate owned life insurance	(0.6		)	(0.5		)	(0.3		)
State income taxes	4.1			1.5			1.9
Other	(0.2		)	(0.1		)	1.1
Income taxes	$	75.7		$	65.5		$	26.1
Effective income tax rate	32.7		%	41.2		%	18.2		%
In 2014, our effective tax rate was 32.7% compared to 41.2% in 2013 and 18.2% in 2012. The prior year effective tax rate reflects incremental US and state income taxes of $23.2 million that we incurred on the sale of our investment in AAE. Additionally, we realized foreign tax credit carryforwards of $3.9 million. In 2012, we recognized a $15.5 million benefit attributable to previously unrecognized tax benefits resulting from the expiration of the applicable statute of limitations. Additionally, the 2012 tax provision benefited from the utilization of $13.7 million in foreign tax credits partially offset by $6.3 million of tax expenses associated with foreign dividends repatriated during the year.
The adjustment for foreign earnings in each year reflects the impact of lower tax rates on income earned at our foreign subsidiaries. State income taxes are recognized on domestic pretax income or loss. The amount of our domestic income subject to state taxes relative to our total worldwide income impacts the effect state income tax has on our overall income tax rate.
Separately, income taxes for our affiliates were $18.3 million in 2014, $16.5 million in 2013, and $2.0 million in 2012. These amounts were favorably impacted by deferred tax benefits of $7.6 million in 2013 and $4.6 million in 2012, which were the result of income tax rate reductions enacted in the United Kingdom.

Concentrations

Concentrations	12 Months Ended
	Dec. 31, 2014
Risks and Uncertainties [Abstract]
Concentrations	Concentration of Revenues
	We derived revenue from a wide range of industries and companies. We generated approximately 24% of our total revenues from customers in the petroleum industry, 21% from the chemical industry, 20% from the transportation industry, 10% from the steel industry, and 7% from the food/agriculture industries. Our foreign identifiable revenues were primarily derived in Germany, Canada, Poland, Mexico, and Austria.
	Concentration of Credit Risk
	We did not have revenue concentrations greater than 10% from any particular customer for the years ended December 31, 2014, 2013, and 2012. Under our lease agreements with customers, we typically retain legal ownership of the assets unless such assets have been financed by sale-leasebacks. We perform a credit evaluation prior to approval of a lease contract. Subsequently, we monitor the creditworthiness of the customer and the value of the collateral on an ongoing basis. We maintain an allowance for losses to provide for credit losses inherent in our reservable assets portfolio.
	Concentration of Labor Force
	As of December 31, 2014, collective bargaining agreements covered approximately 40% of our employees of which agreements covering 3% of employees have expired or will expire within the next year. The hourly employees at our US service centers are represented by the United Steelworkers. Employees at three of Rail North America's Canadian service centers are represented by Unifor, the union formerly known as the Communication, Energy and Paperworkers Union of Canada, and Employee Shop Committee of Riviere-des-Prairies. The unlicensed shipboard personnel on twelve of the ASC vessels in operation during 2014 are represented by the Seafarers International Union. Licensed personnel on ASC’s vessels, other than captains, are represented by the American Maritime Officers. Certain employees of GATX Rail Europe are represented by one union in Germany and three unions in Poland.

Commercial_Commitments

Commercial Commitments	12 Months Ended
	Dec. 31, 2013
Guarantees [Abstract]
Commercial Commitments	We have entered into various commercial commitments, such as guarantees and standby letters of credit, related to certain transactions. These commercial commitments require us to fulfill specific obligations in the event of third party demands. Similar to our balance sheet investments, these commitments expose us to credit, market, and equipment risk. Accordingly, we evaluate these commitments and other contingent obligations using techniques similar to those we use to evaluate funded transactions.
	The following table shows our commercial commitments as of December 31 (in millions):
		2014		2013
	Lease payment guarantees	$	28.5	$	34.8
	Standby letters of credit	8.7		8.8
	Performance bonds	0.4		0.6
	Asset residual value guarantees	—		5.6
	Total commercial commitments (1)	$	37.6	$	49.8
	__________________
	-1	The carrying value of liabilities on the balance sheet for commercial commitments was $5.1 million at December 31, 2014 and $6.2 million at December 31, 2013. The expirations of these commitments range from 2017 to 2023. We are not aware of any event that would require us to satisfy any of our commitments.
	Lease payment guarantees are commitments to financial institutions to make lease payments for a third party in the event they default. We reduce any liability that may result from these guarantees by the value of the underlying asset or group of assets.
	We are also parties to standby letters of credit and performance bonds, which primarily relate to contractual obligations and general liability insurance coverages. No material claims have been made against these obligations, and no material losses are anticipated.
	Asset residual value guarantees are commitments to third parties that an asset or group of assets will be worth a specified value at the end of a lease term. We earn a fee for providing these guarantees, which we amortize into income over the guarantee period. If the assets are disposed of for more than the amount we guaranteed, we receive a share of the proceeds in excess of the guaranteed amount. We record these residual sharing gains in our net gain on asset dispositions. If the net realizable value of the asset is less than the guaranteed amount, we incur a liability for the amount we guaranteed less the value realized from the asset's disposal.

Earnings_Per_Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Earnings Per Share	Earnings per Share
	We compute basic earnings per share by dividing net income available to our common shareholders by the weighted average number of shares of our common stock outstanding. We appropriately weighted shares issued or reacquired during the year for the portion of the year that they were outstanding. Our diluted earnings per share reflect the impacts of our potentially dilutive securities, which include our convertible preferred stock and our equity compensation awards.
	The following table shows the computation of our basic and diluted net income per common share for the years ending December 31 (in millions, except per share amounts):
		2014		2013		2012
	Numerator:
	Net income	$	205	$	169.3	$	137.3
	Denominator:
	Denominator for basic earnings per share — weighted average shares	45		46.4		46.8
	Effect of dilutive securities
	Equity compensation plans	0.8		0.7		0.7
	Convertible preferred stock	—		—		0.1
	Weighted average shares outstanding - diluted	45.8		47.1		47.6
	Basic earnings per share	$	4.55	$	3.64	$	2.93
	Diluted earnings per share	$	4.48	$	3.59	$	2.88

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Our goodwill, all of which pertains to Rail North America and Rail International, was $86.1 million as of December 31, 2014 and $94.6 million as of December 31, 2013. In the fourth quarter of 2014, we performed a review for impairment of goodwill, and concluded that goodwill was not impaired. For 2014 and 2013, changes in the carrying amount of our goodwill resulted from changes in foreign currency exchange rates.

Allowance_for_Losses

Allowance for Losses	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Allowance for Losses	We had total loans outstanding of $97.3 million at December 31, 2014 and $122.7 million at December 31, 2013. No loans were impaired at December 31, 2014 or 2013. In January 2015, Ahaus Alstätter Eisenbahn Cargo AG (“AAE”) repaid its outstanding loan in the amount of of €68.2 million ($77.0 million), including €67.5 million ($76.2 million) of remaining principal and €0.7 million ($0.8 million) of accrued interest.
	The following table shows scheduled loan principal payments due by year at December 31, 2014 (in millions):
	2015	$	86.4
	2016	4.3
	2017	2
	2018	4.6
	2019	—
	Thereafter	—
		$	97.3
	The following table shows changes in the allowance for losses at December 31 (in millions):
		2014			2013
	Beginning balance	$	5.2		$	4.6
	Provision for losses	0.8			0.7
	Charges to allowance	(0.3		)	—
	Recoveries and other, including foreign exchange adjustments	—			(0.1		)
	Ending balance	$	5.7		$	5.2
	The allowance for losses is comprised of a general allowance for trade receivables and specific allowances for finance leases. As of December 31, 2014, the general allowance for trade receivables was $4.5 million, or 5.2% of rent and other receivables, compared to $4.0 million, or 4.9% of rent and other receivables, at December 31, 2013. At December 31, 2014, specific allowances of $1.2 million were comparable to prior year.

Other_Assets_and_Other_Liabili

Other Assets and Other Liabilities	12 Months Ended
	Dec. 31, 2014
Other Assets and Other Liabilities [Abstract]
Other Assets and Other Liabilities	The following table shows the components of other assets reported on our balance sheets as of December 31 (in millions):
		2014		2013
	Inventory	$	52	$	45.8
	Office furniture, fixtures and other equipment, net of accumulated depreciation	34.1		34.9
	Derivatives	11.5		6
	Deferred financing costs	21.6		18.6
	Assets held for sale	7		10.3
	Other investments	6		6.9
	Prepaid items	12.4		12.4
	Prepaid pension	—		32.9
	Other	84.4		57.7
		$	229	$	225.5
	The following table shows the components of other liabilities reported on our balance sheets as of December 31 (in millions):
		2014		2013
	Accrued operating lease expense	$	43.4	$	48.6
	Accrued pension and other post-retirement benefits	86.6		68.2
	Deferred gains on sale-leasebacks	49		53.3
	Unrecognized tax benefits	3.6		3.9
	Environmental accruals	13.8		14.7
	Deferred income	5.6		6.7
	Derivatives	7.5		3.6
	Other	36.6		31.6
		$	246.1	$	230.6

Shareholders_Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Shareholders' Equity	Shareholders’ Equity
	In 2014, our board of directors authorized a $250 million share repurchase program. During the year, we purchased 1.9 million shares of common stock for $124.6 million. In 2013, we purchased 1.4 million shares of common stock for $68.6 million, which completed our $200 million repurchase authorization approved in 2008. The timing of share repurchases depends on market conditions and other factors.
	In accordance with our certificate of incorporation, 120 million shares of common stock are authorized, at a par value of $0.625 per share. As of December 31, 2014, 66.6 million shares were issued and 44.2 million shares were outstanding.
	The following shares of common stock were reserved as of December 31, 2014 (in millions):
	GATX Corporation 2004 Equity Incentive Compensation Plan	2.5
	GATX Corporation 2012 Incentive Award Plan	3.5
		6
	Our certificate of incorporation also authorizes five million shares of preferred stock at a par value of $1.00 per share. As of December 31, 2014, we have no outstanding shares of preferred stock. In 2013, we either converted or redeemed all 15,567 outstanding shares of our $2.50 cumulative convertible preferred stock.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss)
	The following table shows the change in components for accumulated other comprehensive loss (in millions):
		Foreign Currency Translation Gain (Loss)			Unrealized Gain (Loss) on Securities			Unrealized Loss on Derivative Instruments			Post-Retirement Benefit Plans			Total
	Balance at December 31, 2011	$	6.4		$	(0.6	)	$	(56.2	)	$	(118.7	)	$	(169.1	)
	Change in component	25			0.5			6.2			(28.8		)	2.9
	Reclassification adjustments into earnings	—			(0.4		)	6.5			8.7			14.8
	Income tax effect	—			0.1			(1.0		)	7.7			6.8
	Balance at December 31, 2012	31.4			(0.4		)	(44.5		)	(131.1		)	(144.6		)
	Change in component	25.8			1.4			22.3			71			120.5
	Reclassification adjustments into earnings	—			—			6.6			13.8			20.4
	Income tax effect	—			(0.6		)	(6.5		)	(31.9		)	(39.0		)
	Balance at December 31, 2013	57.2			0.4			(22.1		)	(78.2		)	(42.7		)
	Change in component	(79.1		)	(0.2		)	0.3			(57.3		)	(136.3		)
	Reclassification adjustments into earnings	—			—			6			10.1			16.1
	Income tax effect	—			0.1			(3.3		)	17.7			14.5
	Balance at December 31, 2014	$	(21.9	)	$	0.3		$	(19.1	)	$	(107.7	)	$	(148.4	)

Foreign_Operations

Foreign Operations	12 Months Ended
	Dec. 31, 2014
Concentration Risks, Types, No Concentration Percentage [Abstract]
Foreign Operations	For the years ended December 31, 2014, 2013, and 2012, we did not derive revenues in excess of 10% of our consolidated revenues from any one foreign country. Additionally, at December 31, 2014 and 2013, we did not have more than 10% of our identifiable assets in any one foreign country.
	The following table shows our domestic and foreign revenues and identifiable assets for the years ending or as of December 31 (in millions):
		2014		2013		2012
	Revenues
	Foreign	$	346.2	$	332.1	$	279.8
	United States	1,104.80		988.9		963.4
		$	1,451.00	$	1,321.00	$	1,243.20
	Identifiable Assets
	Foreign	$	2,133.90	$	2,200.10	$	1,897.90
	United States	4,803.60		4,349.50		4,157.50
		$	6,937.50	$	6,549.60	$	6,055.40

Legal_Proceedings_and_Other_Co

Legal Proceedings and Other Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings and Other Contingencies	OTE 23. Legal Proceedings and Other Contingencies
	Various legal actions, claims, assessments and other contingencies arising in the ordinary course of business are pending against GATX and certain of our subsidiaries. These matters are subject to many uncertainties, and it is possible that some of these matters could ultimately be decided, resolved or settled adversely.
	Viareggio Derailment
	In June 2009, a train consisting of fourteen liquefied petroleum gas (“LPG”) tank cars owned by GATX Rail Austria GmbH (an indirect subsidiary of the Company, "GATX Rail Austria") and its subsidiaries derailed while passing through the City of Viareggio, in the province of Lucca, Italy. Five tank cars overturned and one of the overturned cars was punctured by a peg or obstacle along the side of the track, resulting in a release of LPG, which subsequently ignited. Thirty-two people died and others were injured in the fire, which also resulted in property damage. The LPG tank cars were leased to FS Logistica S.p.A., a subsidiary of the Italian state-owned railway, Ferrovie dello Stato S.p.A (the “Italian Railway”).
	On December 14, 2012, the Public Prosecutors of Lucca ("Public Prosecutors") formally charged GATX Rail Austria and two of its subsidiaries (collectively, "GRA"), as well as ten maintenance and supervisory employees (the "Employees"), with various negligence-based crimes related to the accident, all of which are punishable under Italian law by incarceration, damages and fines. Similar charges were brought against four Italian Railway companies and eighteen of their employees, among others. The Public Prosecutors assert that the axle on a tank car broke, causing the derailment and resulting in a tank rupture and release of LPG, after the car hit an obstacle placed on the side of the track by the Italian Railway. The Public Prosecutors further allege that a crack in the axle was detectable at the time of final inspection but was overlooked by the Employees at the Jungenthal Waggon GmbH workshop (a subsidiary of GATX Rail Austria). The trial in the Court of Lucca (the “Lucca Trial”) commenced on November 13, 2013.
	With respect to civil claims, GRA’s insurers continue to work cooperatively with the insurer for the Italian Railway to adjust and settle personal injury and property damage claims. These joint settlement efforts have so far settled most of the significant civil claims related to the accident; however, approximately 90 civil claimants did not settle and are currently parties to the Lucca Trial. The Court of Lucca will determine both the civil and criminal liability of the defendants in the one proceeding. GRA expects that its insurers will cover any civil damages if awarded to the claimants in the Lucca trial.
	Since May 2012, one of the excess insurers providing coverage, Liberty Mutual Insurance Europe Limited (“Liberty”), has settled civil claims but has refused to reimburse GRA for its ongoing legal defense fees and costs, taking a position contrary to our other insurers in the prior underlying layers who had provided coverage for such expenses. As of December 31, 2014, GRA had incurred approximately $7.8 million in unreimbursed defense fees and costs, and GRA continues to incur costs in connection with the Lucca Trial. Consequently, in October 2013, GRA filed an arbitration proceeding against Liberty seeking to recoup its unreimbursed defense fees and costs (the “Liberty Arbitration”), which is set for hearing in November 2015. GRA is also negotiating issues of reimbursement for outstanding defense costs with the three other insurers in the current coverage layer, which includes a 25% share held by Liberty. GRA cannot predict the outcome of the Liberty Arbitration or the amount of defense fees and costs that ultimately may not be reimbursed by Liberty or the other excess insurers in the current coverage layer.
	GRA believes that it and its Employees acted diligently and properly, but we cannot predict the outcome of the Lucca Trial or what other legal proceedings or claims, if any, may be initiated against GRA or its personnel, and, therefore, cannot reasonably estimate the possible amount or range of loss that may ultimately be incurred in connection with this accident. Accordingly, we have not established any accruals with respect to this matter.
	Other Litigation
	GATX and its subsidiaries have been named as defendants in various other legal actions and claims, governmental proceedings and private civil suits arising in the ordinary course of business, including environmental matters, workers’ compensation claims and other personal injury claims. Some of these proceedings include claims for punitive as well as compensatory damages.
	Several of our subsidiaries have also been named as defendants or co-defendants in cases alleging injury caused by exposure to asbestos. The plaintiffs seek an unspecified amount of damages based on common law, statutory, or premises liability or, in the case of ASC, the Jones Act, which provides limited remedies to certain maritime employees. As of January 31, 2015, there were 104 asbestos-related cases pending against GATX and its subsidiaries. Of the total number of pending cases, 87 are Jones Act claims, most of which were filed against ASC before the year 2000. During 2014, 7 new cases were filed, and 34 cases were dismissed without payment or otherwise settled for an immaterial amount. In addition, demand has been made against GATX for asbestos-related claims under limited indemnities given in connection with the sale of certain of our former subsidiaries. It is possible that the number of these cases or claims for indemnity could begin to grow and that the cost of these cases, including costs to defend, could correspondingly increase in the future.
	Litigation Accruals
	For losses related to those litigation matters that we believe to be probable and for which an amount of loss can be reasonably estimated, we have recorded accruals totaling $1.7 million at December 31, 2014. However, we cannot determine a reasonable estimate of the maximum possible loss or range of loss for these matters given that they are at various stages of the litigation process and each case is subject to the inherent uncertainties of litigation (such as the strength of our legal defenses and the availability of insurance recovery). Although the maximum amount of liability that may ultimately result from any of these matters cannot be predicted with absolute certainty, management expects that none of the matters for which we have recorded an accrual, when ultimately resolved, will have a material adverse effect on our consolidated financial position or liquidity. It is possible, however, that the ultimate resolution of one or more of these matters could have a material adverse effect on our results of operations in a particular quarter or year if such resolution results in liability that materially exceeds the accrued amount.
	In addition, we have other litigation matters pending for which we have not recorded any accruals because our potential liability for those matters is not probable or cannot be reasonably estimated based on currently available information. For those matters where we have not recorded an accrual but a loss is reasonably possible, we cannot determine a reasonable estimate of the maximum possible loss or range of loss for these matters given that they are at various stages of the litigation process and each case is subject to the inherent uncertainties of litigation (such as the strength of our legal defenses and the availability of insurance recovery). Although the maximum amount of liability that may ultimately result from any of these matters cannot be predicted with absolute certainty, management expects that none of the matters for which we have not recorded an accrual, when ultimately resolved, will have a material adverse effect on our consolidated financial position or liquidity. It is possible, however, that the ultimate resolution of one or more of these matters could have a material adverse effect on our results of operations in a particular quarter or year if such resolution results in a significant liability for GATX.
	Environmental
	Our operations are subject to extensive federal, state and local environmental regulations. Our operating procedures include practices to protect the environment from the risks inherent in full service railcar leasing, which involves maintaining railcars used by customers to transport chemicals and other hazardous materials. Additionally, some of our real estate holdings, including previously owned properties, are or have been used for industrial or transportation-related purposes or leased to commercial or industrial companies whose activities might have resulted in discharges on the property. As a result, we are subject to environmental cleanup and enforcement actions. In particular, the federal Comprehensive Environmental Response, Compensation and Liability Act (“CERCLA”), also known as the Superfund law, as well as similar state laws, impose joint and several liability for cleanup and enforcement costs on current and former owners and operators of a site without regard to fault or the legality of the original conduct. If there are other potentially responsible parties (“PRPs”), we generally contribute to the cleanup of these sites through cost-sharing agreements with terms that vary from site to site. Costs are typically allocated based on the relative volumetric contribution of material, the period of time the site was owned or operated, and/or the portion of the site owned or operated by each PRP.
	At the time a potential environmental issue is identified, initial accruals for environmental liability are established when such liability is determined to be probable and a reasonable estimate of the associated costs can be made. Costs are estimated based on the type and level of investigation and/or remediation activities that our internal environmental staff (and where appropriate, independent consultants) have advised to be necessary to comply with applicable laws and regulations. Activities include surveys and environmental studies of potentially contaminated sites as well as costs for remediation and restoration of sites determined to be contaminated. In addition, we have provided indemnities for potential environmental liabilities to buyers of divested companies. In these instances, accruals are based on the scope and duration of the respective indemnities together with the extent of known contamination. Estimates are periodically reviewed and adjusted as required to reflect additional information about facility or site characteristics or changes in regulatory requirements. We conduct a quarterly environmental contingency analysis, which considers a combination of factors including independent consulting reports, site visits, legal reviews, analysis of the likelihood of participation in and the ability of other PRPs to pay for cleanup, and historical trend analyses.
	We are involved in administrative and judicial proceedings and other voluntary and mandatory cleanup efforts at 18 sites, including Superfund sites, for which we are contributing to the cost of performing the study or cleanup, or both, of alleged environmental contamination. As of December 31, 2014, we have recorded accruals of $13.8 million for remediation and restoration costs that we believe to be probable and for which the amount of loss can be reasonably estimated. These amounts are included in other liabilities on our balance sheet. Our environmental liabilities are not discounted.
	We did not materially change our methodology for identifying and calculating environmental liabilities in the last three years. Currently, no known trends, demands, commitments, events or uncertainties exist that are reasonably likely to occur and materially affect the methodology or assumptions described above.
	The recorded accruals represent our best estimate of all costs for remediation and restoration of affected sites, without reduction for anticipated recoveries from third parties, and include both asserted and unasserted claims. However, we are unable to provide a reasonable estimate of the maximum potential loss associated with these sites because cleanup costs cannot be predicted with certainty. Various factors beyond our control can impact the amount of loss GATX will ultimately incur with respect to these sites, including the extent of corrective actions that may be required; evolving environmental laws and regulations; advances in environmental technology, the extent of other parties' participation in cleanup efforts; developments in periodic environmental analyses related to sites determined to be contaminated, and developments in environmental surveys and studies of potentially contaminated sites. As a result, future charges associated with these sites could have a significant effect on results of operations in a particular quarter or year if the costs materially exceed the accrued amount as individual site studies and remediation and restoration efforts proceed. However, management believes it is unlikely that the ultimate cost to GATX for any of these sites, either individually or in the aggregate, will have a material adverse effect on our consolidated financial position or liquidity.

Financial_Data_of_Business_Seg

Financial Data of Business Segments	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Financial Data of Business Segments	Financial Data of Business Segments
	The financial data presented below depicts the profitability, financial position, and capital expenditures of each of our business segments.
	We lease, operate, manage, and remarket long-lived, widely-used assets, primarily in the rail and marine markets. We also invest in joint ventures that complement our existing business activities. We report our financial results through four primary business segments: Rail North America, Rail International, American Steamship Company (“ASC”), and Portfolio Management.
	Rail North America is comprised of our wholly owned operations in the United States, Canada, and Mexico, as well as an affiliate investment. Rail North America primarily provides railcars pursuant to full-service leases under which it maintains the railcars, pays ad valorem taxes and insurance, and provides other ancillary services.
	Rail International is comprised of our wholly owned European operations ("GATX Rail Europe" or "GRE") and a recently established railcar leasing business in India ("Rail India"), as well as one development stage affiliate in China. GRE leases railcars to customers throughout Europe pursuant to full-service leases under which it maintains the railcars and provides insurance and other ancillary services.
	ASC operates the largest fleet of US-flagged vessels on the Great Lakes, providing waterborne transportation of dry bulk commodities such as iron ore, coal, limestone aggregates, and metallurgical limestone.
	Portfolio Management generates leasing, marine operating, asset remarketing and management fee income through a collection of diversified wholly owned assets and joint venture investments.
	Segment profit is an internal performance measure used by the Chief Executive Officer to assess the performance of each segment in a given period. Segment profit includes all revenues, pretax earnings from affiliates, and net gains on asset dispositions that are attributable to the segments, as well as expenses that management believes are directly associated with the financing, maintenance, and operation of the revenue earning assets. Segment profit excludes selling, general and administrative expenses, income taxes, and certain other amounts not allocated to the segments. These amounts are included in Other.
	We allocate debt balances and related interest expense to each segment based upon a predetermined fixed recourse leverage level expressed as a ratio of recourse debt (including off-balance-sheet debt) to equity. The leverage levels are 5:1 for Rail North America, 2:1 for Rail International, 1.5:1 for ASC, and 3:1 for Portfolio Management. We believe that by using this leverage and interest expense allocation methodology, each operating segment’s financial performance reflects appropriate risk-adjusted borrowing costs.
	The following tables show certain segment data for the years ended December 31, 2014, 2013, and 2012 (in millions):
		Rail North America			Rail International			ASC			Portfolio Management			Other			GATX Consolidated
	2014 Profitability
	Revenues
	Lease revenue	$	864.1		$	188.6		$	4.2		$	29.7		$	—		$	1,086.60
	Marine operating revenue	—			—			223			63.3			—			286.3
	Other revenue	63.4			10.3			—			4.4			—			78.1
	Total Revenues	927.5			198.9			227.2			97.4			—			1,451.00
	Expenses
	Maintenance expense	265.5			45.9			25.6			—			—			337
	Marine operating expense	—			—			149.2			48.6			—			197.8
	Depreciation expense	190			47.1			13.6			22.8			—			273.5
	Operating lease expense	103.7			—			5.2			—			(0.2		)	108.7
	Other operating expense	21.9			5.1			—			1.9			—			28.9
	Total Expenses	581.1			98.1			193.6			73.3			(0.2		)	945.9
	Other Income (Expense)
	Net gain (loss) on asset dispositions	72.3			6			(0.5		)	9.4			—			87.2
	Interest expense, net	(98.4		)	(24.7		)	(5.6		)	(24.3		)	(5.4		)	(158.4		)
	Other expense	(7.2		)	(3.1		)	(0.2		)	(1.2		)	(1.8		)	(13.5		)
	Share of affiliates' earnings (pretax)	7.9			(0.3		)	—			60.2			—			67.8
	Segment profit (loss)	$	321		$	78.7		$	27.3		$	68.2		$	(7.0	)	488.2
	Selling, general and administrative expense																189.2
	Income taxes (including $18.3 related to affiliates' earnings)																94
	Net income																$	205
	Selected Balance Sheet Data
	Investments in affiliated companies	$	17.2		$	1.8		$	—		$	338.7		$	—		$	357.7
	Identifiable assets	$	4,358.30		$	1,229.40		$	286.7		$	813.3		$	249.8		$	6,937.50
	Capital Expenditures
	Portfolio investments and capital additions	$	810.6		$	163.6		$	18.4		$	32.3		$	5.6		$	1,030.50
														Other			GATX Consolidated
		Rail North America			Rail International			ASC			Portfolio Management
	2013 Profitability
	Revenues
	Lease revenue	$	758.9		$	180.2		$	4.2		$	31.9		$	—		$	975.2
	Marine operating revenue	—			—			223.5			51.6			—			275.1
	Other revenue	58.2			8.8			—			3.7			—			70.7
	Total Revenues	817.1			189			227.7			87.2			—			1,321.00
	Expenses
	Maintenance expense	228.2			42.9			22.9			—			—			294
	Marine operating expense	—			—			151.3			38.5			—			189.8
	Depreciation expense	176.7			43.2			12.1			23			—			255
	Operating lease expense	124.4			—			5.2			—			(0.2		)	129.4
	Other operating expense	18.4			5.3			—			2.4			—			26.1
	Total Expenses	547.7			91.4			191.5			63.9			(0.2		)	894.3
	Other Income (Expense)
	Net gain (loss) on asset dispositions	67.7			3.7			(1.3		)	15.5			—			85.6
	Interest expense, net	(106.0		)	(23.9		)	(6.2		)	(26.7		)	(3.8		)	(166.6		)
	Other (expense) income	(9.8		)	(1.1		)	0.2			1.4			0.9			(8.4		)
	Share of affiliates' earnings (pretax)	10.3			21.1			—			60.9			—			92.3
	Segment profit (loss)	$	231.6		$	97.4		$	28.9		$	74.4		$	(2.7	)	429.6
	Selling, general and administrative expense																178.3
	Income taxes (including $16.5 related to affiliates' earnings)																82
	Net income																$	169.3
	Selected Balance Sheet Data
	Investments in affiliated companies	$	31.4		$	2		$	—		$	320.9		$	—		$	354.3
Identifiable assets	$	3,710.50		$	1,297.10		$	271		$	856.9		$	414.1		$	6,549.60
Capital Expenditures
Portfolio investments and capital additions	$	502.4		$	168.5		$	11.2		$	170.5		$	7		$	859.6
													Other			GATX Consolidated
	Rail North America			Rail International			ASC			Portfolio Management
2012 Profitability
Revenues
Lease revenue	$	713.9		$	161.2		$	4.3		$	37.6		$	—		$	917
Marine operating revenue	—			—			239.1			26.4			—			265.5
Other revenue	51.4			6.5			—			2.8			—			60.7
Total Revenues	765.3			167.7			243.4			66.8			—			1,243.20
Expenses
Maintenance expense	201.4			46.6			21.7			—			—			269.7
Marine operating expense	—			—			160.3			22.1			—			182.4
Depreciation expense	167.7			36.1			11.9			21.7			—			237.4
Operating lease expense	126.5			—			3.8			0.2			(0.3		)	130.2
Other operating expense	18.5			5.1			(0.3		)	0.9			0			24.2
Total Expenses	514.1			87.8			197.4			44.9			(0.3		)	843.9
Other Income (Expense)
Net gain on asset dispositions	58.6			1.7			—			19.2			—			79.5
Interest expense, net	(101.9		)	(24.5		)	(7.1		)	(27.7		)	(5.4		)	(166.6		)
Other (expense) income	(5.1		)	(6.1		)	(1.4		)	3.4			1			(8.2		)
Share of affiliates' earnings (pretax)	6.5			(18.3		)	—			33.4			—			21.6
Segment profit (loss)	$	209.3		$	32.7		$	37.5		$	50.2		$	(4.1	)	325.6
Selling, general and administrative expense																160.2
Income taxes (including $2.0 related to affiliates' earnings)																28.1
Net income																$	137.3
Selected Balance Sheet Data
Investments in affiliated companies	$	46.9		$	77.2		$	—		$	377.9		$	—		$	502
Identifiable assets	$	3,601.10		$	1,105.80		$	284.2		$	797.4		$	266.9		$	6,055.40
Capital Expenditures
Portfolio investments and capital additions	$	465.9		$	200.1		$	12.6		$	83.5		$	7.9		$	770

Subsequent_Events

Subsequent Events	12 Months Ended
	Dec. 31, 2014
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent to December 31, 2014, we issued $100 million of 2.60% senior notes due in 2020, $300 million of 3.25% senior notes due in 2025 and $250 million of 4.50% senior notes due in 2045. We intend to use the net proceeds for several purposes, including the repayment of outstanding debt principal or term loan balances and for general corporate purposes, including working capital and capital expenditures.

Schedule_I_Condensed_Financial

Schedule I - Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Information of Registrant	SCHEDULE I — CONDENSED FINANCIAL INFORMATION OF REGISTRANT
	GATX CORPORATION
	(Parent Company)
	BALANCE SHEETS
	(In millions)
		31-Dec
		2014			2013
	Assets
	Cash and cash equivalents	$	162.3		$	294.6
	Operating assets and facilities, net	3,397.00			2,724.30
	Investments in affiliated companies	2,199.50			2,197.90
	Other assets	396			428.8
	Total Assets	$	6,154.80		$	5,645.60
	Liabilities and Shareholders’ Equity
	Accounts payable and accrued expenses	$	54.9		$	79.6
	Debt	3,821.10			3,249.20
	Other liabilities	964.8			919.8
	Total Liabilities	4,840.80			4,248.60
	Total Shareholders’ Equity	1,314.00			1,397.00
	Total Liabilities and Shareholders’ Equity	$	6,154.80		$	5,645.60
	See accompanying note to condensed financial statements.
	SCHEDULE I — CONDENSED FINANCIAL INFORMATION OF REGISTRANT (CONT’D)
	GATX CORPORATION
	(Parent Company)
	STATEMENTS OF COMPREHENSIVE INCOME
	(In millions)
		Year Ended December 31
		2014			2013			2012
	Revenues
	Lease revenue	$	669.7		$	543		$	504.5
	Other revenue	60.2			51.3			43.5
	Total Revenues	729.9			594.3			548
	Expenses
	Maintenance expense	227.6			176.5			154.8
	Depreciation expense	147.7			131.1			122.2
	Operating lease expense	83			89.5			91.6
	Other operating expense	17.1			12.7			12
	Selling, general and administrative expense	139.7			131.1			118.4
	Total Expenses	615.1			540.9			499
	Other Income (Expense)
	Net gain on asset dispositions	67.9			68.6			59.4
	Interest expense, net	(66.7		)	(63.7		)	(65.4		)
	Other income (expense)	2.5			(7.0		)	(4.4		)
	Income before Income Taxes and Share of Affiliates' Earnings	118.5			51.3			38.6
	Income Taxes	(41.7		)	(10.7		)	1
	Share of Affiliates' Earnings, Net of Taxes	128.2			128.7			97.7
	Net Income	$	205		$	169.3		$	137.3
	Other Comprehensive Income, Net of Taxes
	Foreign currency translation adjustments	(79.1		)	25.8			25
	Unrealized (loss) gain on securities	(0.1		)	0.8			0.2
	Unrealized gain on derivative instruments	3			22.4			11.7
	Post-retirement benefit plans	(29.5		)	52.9			(12.4		)
	Other comprehensive (loss) income	(105.7		)	101.9			24.5
	Comprehensive Income	$	99.3		$	271.2		$	161.8
	See accompanying note to condensed financial statements.
	SCHEDULE I — CONDENSED FINANCIAL INFORMATION OF REGISTRANT (CONT’D)
	GATX CORPORATION
	(Parent Company)
	STATEMENTS OF CASH FLOWS
	(In millions)
		Year Ended December 31
		2014			2013			2012
	Operating Activities
	Net cash provided by operating activities	$	219.5		$	104.3		$	269.6
Investing Activities
Capital additions	(748.1		)	(513.5		)	(444.6		)
Purchases of leased-in assets	(150.5		)	(61.4		)	(1.4		)
Proceeds from sale-leasebacks	—			90.7			104.9
Portfolio proceeds and other	169.5			320.7			136.6
Net cash used in investing activities	(729.1		)	(163.5		)	(204.5		)
Financing Activities
Repayments of debt (original maturities longer than 90 days)	(692.2		)	(483.8		)	(603.7		)
Net increase (decrease) in debt with original maturities of 90 days or less	69			(185.0		)	185
Proceeds from issuances of debt (original maturities longer than 90 days)	1,188.70			967			381.4
Stock repurchased	(124.6		)	(68.6		)	—
Dividends	(62.0		)	(60.5		)	(57.7		)
Other	(1.6		)	1.2			5
Net cash provided by (used in) financing activities	377.3			170.3			(90.0		)
Net (decrease) increase in cash and cash equivalents during the year	(132.3		)	111.1			(24.9		)
Cash and Cash Equivalents at beginning of year	294.6			183.5			208.4
Cash and Cash Equivalents at end of year	$	162.3		$	294.6		$	183.5
See accompanying note to condensed financial statements.
Note to Condensed Financial Statements
Basis of Presentation
The condensed financial statements represent the Balance Sheets, Statements of Comprehensive Income and Cash Flows of GATX Corporation, the parent company. In these parent-company-only financial statements, our investment in subsidiaries and joint ventures (collectively "affiliates") is stated at cost plus equity in undistributed earnings of affiliates since the date of acquisition. Our share of net income from affiliates is included in consolidated net income using the equity method. The parent-company-only financial statements should be read in conjunction with our consolidated financial statements.

Significant_Accounting_Policie1

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Basis of presentation	Basis of Presentation
	We prepared the accompanying consolidated financial statements in accordance with US GAAP. Certain prior year amounts may have been reclassified to conform to the 2014 presentation.
Use of Estimates	Use of Estimates
	Preparing financial statements in accordance with GAAP requires us to make estimates and assumptions that affect the amounts we report. We regularly evaluate our estimates and judgments based on historical experience and other relevant facts and circumstances. Actual amounts could differ from our estimates.
Consolidation	Consolidation
	Our consolidated financial statements include our assets, liabilities, revenues, and expenses, as well as the assets, liabilities, revenues, and expenses of subsidiaries in which we have a controlling financial interest and variable interest entities for which we are the primary beneficiary. We have eliminated intercompany transactions and balances. Our consolidated subsidiaries include the following wholly owned, bankruptcy-remote special purpose corporations that finance and lease railcars: General American Railcar Corporation, General American Railcar Corporation III, General American Marks Company, and GARC LLC. The debt and lease obligations of these special purpose corporations are nonrecourse to us, and their assets are available first to satisfy claims of their creditors.
Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block]	Our consolidated financial statements include our assets, liabilities, revenues, and expenses, as well as the assets, liabilities, revenues, and expenses of subsidiaries in which we have a controlling financial interest and variable interest entities for which we are the primary beneficiary. We have eliminated intercompany transactions and balances. Our consolidated subsidiaries include the following wholly owned, bankruptcy-remote special purpose corporations that finance and lease railcars: General American Railcar Corporation, General American Railcar Corporation III, General American Marks Company, and GARC LLC. The debt and lease obligations of these special purpose corporations are nonrecourse to us, and their assets are available first to satisfy claims of their creditors.
Investments in Affiliated Companies	Investments in Affiliates
	We use the equity method to account for investments in joint ventures and other unconsolidated entities if we have the ability to exercise significant influence over the financial and operating policies of those investees. Under the equity method, we record our initial investments in these entities at cost and subsequently adjust the investment for our share of the affiliates’ undistributed earnings (losses), and distributions. We include loans to and from affiliates as part of our investment in the affiliate and include interest on any such loans in our share of the affiliates’ earnings. We review the carrying amount of our investments in affiliates annually, or whenever circumstances indicate that the value of these investments may have declined. If we determine an investment is impaired on an other-than-temporary basis, we record a loss equal to the difference between the fair value of the investment and its carrying value. See "Note 7. Investments in Affiliated Companies."
Variable Interest Entities	Variable Interest Entities
	We evaluate whether an entity is a variable interest entity based on the sufficiency of the entity’s equity and by determining whether the equity holders have the characteristics of a controlling financial interest. To determine if we are the primary beneficiary of a variable interest entity, we assess whether we have the power to direct the activities that most significantly impact the economic performance of the entity as well as the obligation to absorb losses or the right to receive benefits that may be significant to the entity. These determinations are both qualitative and quantitative, and they require us to make judgments and assumptions about the entity’s forecasted financial performance and the volatility inherent in those forecasted results. We evaluate new investments for variable interest entity determination and regularly review all existing entities for events that may result in an entity becoming a variable interest entity or us becoming the primary beneficiary of an existing variable interest entity. See "Note 8. Variable Interest Entities."
Fair Value Measurements	Fair Value Measurements
	Fair value is the price that a market participant would receive to sell an asset or pay to transfer a liability in an orderly transaction at the measurement date. We classify fair value measurements according to the three-level hierarchy defined by GAAP, and those classifications are based on our judgment about the reliability of the inputs we use in the fair value measurement. Level 1 inputs are quoted prices available in active markets for identical assets or liabilities. Level 2 inputs are observable, either directly or indirectly, and may include quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data. For assets or liabilities with a specified contractual term, Level 2 inputs must be observable for substantially the full term of that asset or liability. Level 3 inputs are unobservable, meaning they are supported by little or no market activity. Fair value measurements classified as Level 3 typically rely on pricing models and discounted cash flow methodologies, both of which require significant judgment. See "Note 10. Fair Value Disclosure
Cash and Cash Equivalents	Cash and Cash Equivalents
	We classify all highly liquid investments with a maturity of three months or less when purchased as cash equivalents
Restricted cash	Restricted Cash
	Restricted cash is cash and cash equivalents that are restricted as to withdrawal and use. Our restricted cash primarily relates to contractually required cash amounts we maintain for two wholly owned bankruptcy-remote, special purpose corporations.
Operating Assets and Facilities	Operating Assets and Facilities
	We state operating assets, facilities, and capitalized improvements at cost. We include assets we acquire under capital leases in operating assets, and we record the related obligations as liabilities. We depreciate operating assets and facilities over their estimated useful lives or lease terms to estimated residual values using the straight-line method. We depreciate leasehold improvements over the shorter of their useful lives or the lease term. Our estimated depreciable lives of operating assets and facilities are as follows:
	Railcars	27–42 years
	Locomotives	10–20 years
	Buildings	40–50 years
	Leasehold improvements	5–15 years
	Marine vessels	30–65 years
	Other equipment	5–30 years
	We review long-lived assets for impairment whenever circumstances indicate that the carrying amount of those assets may not be recoverable. We evaluate the recoverability of assets to be held and used by comparing the carrying amount of the asset to the undiscounted future net cash flows we expect the asset to generate. If we determine an asset is impaired, we recognize an impairment loss equal to the amount the carrying amount exceeds the asset’s fair value. We classify assets we plan to sell or otherwise dispose of as held for sale, provided they meet specified accounting criteria, and we record those assets at the lower of their carrying amount or fair value less costs to sell
Lease Classification	Lease Classification
	We determine the classification of a lease at its inception. If the provisions of the lease subsequently change, other than by renewal or extension, we evaluate whether that change would have resulted in a different lease classification had the change been in effect at inception. If so, the revised agreement is considered a new lease for lease classification purposes. See "Note 5. Leases."
	Operating Leases
	We offer full-service and net operating leases. We price full-service leases as an integrated service that includes amounts related to executory costs, such as maintenance, insurance, and ad valorem taxes. We do not offer stand-alone maintenance service contracts and are unable to separate executory costs from full-service lease revenue. We recognize operating lease revenue, including amounts related to executory costs, on a straight-line basis over the term of the underlying lease. As a result, we may not recognize lease revenue in the same period as maintenance and other executory costs, which we expense as incurred. See "Note 5. Leases."
	Finance Leases
	For finance leases, we record a gross lease payment receivable and an estimated residual value, net of unearned income. For sales-type leases, we may also recognize a gain or loss in the period the lease is recorded. Gross lease payment receivables are the rents we expect to receive through the end of the lease term for a leased asset. Estimated residual values are our estimates of value of an asset at the end of a finance lease term. We review our estimates of residual values annually or whenever circumstances indicate that residual values may have declined. Other-than-temporary declines in value are recognized as impairments. Initial unearned income is the amount that the original lease payment receivable and the estimated residual value of the leased asset exceeds the original cost or carrying value of the leased asset. We amortize unearned income to lease revenue using the interest method, which produces a constant yield over the lease term. We also defer the initial direct costs related to our direct finance leases and amortize those costs over the lease term as an adjustment to lease revenue.
	We regularly review the finance lease portfolio and classify finance leases as non-performing if it is probable that we will be unable to collect all amounts due under the lease. We generally stop accruing income on non-performing finance leases until all contractual payments are current. We apply payments we receive for non-performing finance leases to the lease payment receivable. See "Note 5. Leases."
Loans	Loans
	We record loans at their principal amount outstanding adjusted for allowances, deferred fees, unamortized premiums or discounts, and accrued interest. We review the loan portfolio regularly and classify a loan as impaired when it is probable that we will be unable to collect all amounts due under the loan agreement. Since most loans are collateralized, we generally measure impairment as the amount the carrying value of the loan exceeds the expected repayments, including any value attributable to underlying collateral. We do not typically recognize interest income on impaired loans until the loan has been paid to contractually current status. We offset loan origination fees by the related direct loan origination costs for a given loan and amortize the net amount of those costs over the term of the loan as an adjustment to interest income. See "Note 6. Loans."
Allowance for Losses	Allowance for Losses
	The allowance for losses is our estimate of credit losses associated with reservable assets. Reservable assets are divided into two categories: rent and other receivables, which includes short-term trade billings, and loans and finance lease receivables. We base our loss reserves for rent and other receivables on historical loss experience and judgments about the impact of economic conditions, the state of the markets we operate in, and collateral values, if applicable. In addition, we may establish specific reserves for known troubled accounts. We evaluate reserve estimates for loans and finance lease receivables on a customer-specific basis, considering each customer's particular credit situation. We also consider the factors we use to evaluate rent and other receivables, which are outlined above. We charge amounts against the allowance when we deem them uncollectable. We made no material changes in our estimation methods or assumptions for the allowance during 2014. We believe that the allowance is adequate to cover losses inherent in our reservable assets as of December 31, 2014. Since the allowance is based on judgments and estimates, it is possible that actual losses incurred will differ from the estimate. See "Note 18. Allowance for Losses."
Goodwill	Goodwill
	We recognize goodwill when the consideration paid to acquire a business exceeds the fair value of the net assets acquired.  We assign goodwill to the same reporting unit as the net assets of the acquired business and we assess our goodwill for impairment on an annual basis in the fourth quarter, or during interim periods if impairment indicators are present. If the carrying amount of the applicable reporting unit exceeds its fair value, we compare the implied fair value of the reporting unit’s goodwill with the carrying amount of goodwill. We record an impairment loss if the carrying amount of goodwill exceeds its implied fair value. The fair values of our reporting units are determined using discounted cash flow models. See "Note 17. Goodwill.
Income Taxes	Income Taxes
	We calculate provisions for federal, state, and foreign income taxes on our reported income before income taxes. We base our calculations of deferred tax assets and liabilities on the differences between the financial statement and tax bases of assets and liabilities, using enacted rates in effect for the year we expect the differences will reverse. We reflect the cumulative effect of changes in tax rates from those we previously used to determine deferred tax assets and liabilities in the provision for income taxes in the period the change is enacted. Provisions for income taxes in any given period differ from those currently payable or receivable because certain items of income and expense are recognized in different periods for financial reporting purposes than for income tax purposes. We may deduct expenses or defer income attributable to uncertain tax positions for tax purposes, however, we have not recognized a tax benefit in the financial statements for those items. We include our liability for uncertain tax positions in other liabilities on the balance sheet. See "Note 13. Income Taxes."
Derivatives	Derivatives
	We use derivatives, such as interest rate swap agreements, Treasury rate locks, options, and currency forwards, to hedge our exposure to interest rate and foreign currency exchange rate risk on existing and anticipated transactions. We formally designate derivatives that meet specific accounting criteria as qualifying hedges at inception. These criteria require us to have the expectation that the derivative will be highly effective at offsetting changes in the fair value or expected cash flows of the hedged exposure, both at the inception of the hedging relationship and on an ongoing basis.
	We recognize all derivative instruments at fair value and classify them on the balance sheet as either other assets or other liabilities. We generally base the classification of derivative activity in the statements of comprehensive income and cash flows on the nature of the hedged item. For derivatives we designate as fair value hedges, we recognize changes in the fair value of both the derivative and the hedged item in earnings. For derivatives we designate as cash flow hedges, we record the effective portion of the change in the fair value of the derivative as part of other comprehensive income (loss), and we recognize those changes in earnings in the period the hedged transaction affects earnings. We recognize any ineffective portion of the change in the fair value of the derivative immediately in earnings. Although we do not hold or issue derivative financial instruments for purposes other than hedging, we do not designate certain derivatives as accounting hedges. We recognize changes in the fair value of these derivatives in earnings immediately. We classify gains and losses on derivatives that are not designated as hedges as other expenses, and we include the related cash flows in cash flows from operating activities. See "Note 10. Fair Value Disclosure
Defined Benefit Pension and Other Post-Retirement Plans	Defined Benefit Pension and Other Post-Retirement Plans
	Our balance sheet reflects the funded status of our pension and post-retirement plans, which is the difference between the fair value of the plan assets and the projected benefit obligation. We recognize the aggregate overfunding of any plans in other assets, the aggregate underfunding of any plans in other liabilities, and the corresponding adjustments for unrecognized actuarial gains (losses) and prior service cost (credits) in accumulated other comprehensive income (loss). See "Note 11. Pension and Other Post-Retirement Benefits."
Foreign Currency	Foreign Currency
	We translate the assets and liabilities of our operations that have non-US dollar functional currencies at exchange rates in effect at year-end. Revenue, expenses, and cash flows are translated monthly using average exchange rates. We defer gains and losses resulting from foreign currency translation and record those gains and losses as a separate component of accumulated other comprehensive income (loss). Gains and losses resulting from foreign currency transactions and from the remeasurement of non-functional currency assets and liabilities are recorded net of related hedges in other expense during the periods in which they occur. Net (losses) gains were $(3.4) million, $2.1 million and $0.5 million for 2014, 2013, and 2012.
Environmental Liabilities	Environmental Liabilities
	We record accruals for environmental remediation costs at sites relating to past or discontinued operations when they are probable and when we can reasonably estimate the expected costs. We record adjustments to initial estimates as necessary. Since these accruals are based on estimates, actual environmental remediation costs may differ. We expense or capitalize environmental remediation costs related to current or future operations as appropriate. See "Note 23. Legal Proceedings and Other Contingencies.
Revenue Recognition	Marine Operating Revenue
	We recognize marine operating revenue as we perform shipping services, and we allocate revenue among reporting periods based on the relative transit time in each reporting period for shipments in process.
	Other Revenue
	We include customer liability repair revenue, fee income, interest on loans, and other miscellaneous revenues in other revenue. We recognize these revenues when earned, which, in the case of management fees we receive from affiliates, is when we perform the related services.
Interest expense, net	Interest Expense, net
	Interest expense is the interest we accrue on indebtedness and the amortization of debt issuance costs and debt discounts. We defer debt issuance costs and discounts and amortize them over the term of the related debt. We report interest expense net of interest income on bank deposits. Interest income on bank deposits was $0.9 million in 2014, $1.2 million in 2013, and $1.9 million in 2012.
Operating Lease Expense	Operating Lease Expense
	We classify leases of certain railcars and other assets and facilities, such as maintenance facilities and equipment, as operating leases. We record the lease expense associated with these leases on a straight-line basis. We defer gains and financing costs associated with sale-leasebacks and amortize those gains and costs as a component of operating lease expense over the related leaseback term. We also classify our leases of office facilities and related administrative assets as operating leases, and we record the associated expense in selling, general and administrative expense. See "Note 5. Leases."
Maintenance and Repair Costs	Maintenance and Repair Costs
	We expense maintenance and repair costs as incurred. We capitalize certain costs incurred in connection with planned major maintenance activities if those activities improve the asset or extend its useful life. We depreciate those capitalized costs over the estimated useful life of the improvement. We capitalize required regulatory survey costs for vessels and amortize those costs over the applicable survey period, which is generally five years.
ASC Expense Seasonality	ASC Expense Seasonality
	ASC's sailing season runs from April 1 to December 31 of each year. We defer certain indirect expenses incurred prior to the beginning of the sailing season, such as winter maintenance, insurance, operating lease expense, and depreciation and amortize them ratably over the sailing season.
Share-Based Compensation	Share-Based Compensation
	We base our measurement of share-based compensation expense on the grant date fair value of an award, and we recognize the expense net of estimated forfeitures over the requisite service period. Forfeiture rates at grant date are initially based on historical experience and are adjusted in subsequent periods if actual experience differs from the estimate. We record a final adjustment when those awards vest. See "Note 12. Share-Based Compensation
Net Gain on Asset Dispositions	Net Gain on Asset Dispositions
	Net gain on disposition includes gains on sales of operating assets and residual sharing income, which we also refer to as asset remarketing income; non-remarketing disposition gains, primarily from scrapping of railcars; and asset impairment losses. We recognize disposition gains, including non-remarketing gains, upon completion of the sale or scrapping of operating assets. Residual sharing income includes fees we receive from the sale of managed assets and assets subject to residual value guarantees, and we recognize these fees upon completion of the underlying transactions.
Other Income (Expense)	Other Income (Expense)
	We include fair value adjustments on certain financial instruments, gains and/or losses on foreign currency transactions and remeasurements, legal defense costs and litigation settlements, along with other miscellaneous income and expense items in other income (expense).

Significant_Accounting_Policie2

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Estimated lives of useful depreciable assets	Operating Assets and Facilities
	We state operating assets, facilities, and capitalized improvements at cost. We include assets we acquire under capital leases in operating assets, and we record the related obligations as liabilities. We depreciate operating assets and facilities over their estimated useful lives or lease terms to estimated residual values using the straight-line method. We depreciate leasehold improvements over the shorter of their useful lives or the lease term. Our estimated depreciable lives of operating assets and facilities are as follows:
	Railcars	27–42 years
	Locomotives	10–20 years
	Buildings	40–50 years
	Leasehold improvements	5–15 years
	Marine vessels	30–65 years
	Other equipment	5–30 years
Net gain on disposition of assets	The following table presents the net gain on asset dispositions for the years ending December 31 (in millions):
		2014			2013			2012
	Disposition gains	$	63.1		$	60		$	42.7
	Residual sharing income	9.4			10.8			22.6
	Non-remarketing disposition gains	16			20.7			19.2
	Asset impairment losses	(1.3		)	(5.9		)	(5.0		)
	Net Gain on Asset Dispositions	$	87.2		$	85.6		$	79.5

Supplemental_Cash_Flow_and_Non1

Supplemental Cash Flow and Noncash Investing Transactions (Tables)	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information
		2014		2013		2012
	Supplemental Cash Flow Information (in millions)
	Interest paid (1)	$	142.6	$	148.7	$	162.3
	Income taxes paid, net	18.7		7.4		11.1
	________
	-1	Interest paid consisted of interest on debt obligations, interest rate swaps (net of interest received), and capital leases. The interest expense we capitalized as part of the cost of construction of major assets was immaterial for all periods presented.

Leases_Tables

Leases (Tables)	12 Months Ended
	Dec. 31, 2014
Leases [Abstract]
Components of GATX's finance leases	GATX as Lessor
	The following table shows the components of our direct finance leases as of December 31 (in millions):
		2014			2013
	Total contractual lease payments receivable	$	204.8		$	270.2
	Estimated unguaranteed residual value of leased assets	68.5			79.8
	Unearned income	(98.6		)	(142.7		)
	Finance leases	$	174.7		$	207.3
Minimum Future Receipts	The following table shows our future contractual receipts from finance leases and noncancelable operating leases as of December 31, 2014 (in millions):
		Finance Leases			Operating Leases (1)			Total
	2015	$	26.3		$	923.4		$	949.7
	2016	25.2			740.3			765.5
	2017	23.9			584.1			608
	2018	22.2			464.7			486.9
	2019	11.8			370			381.8
	Years thereafter	95.4			770.4			865.8
		$	204.8		$	3,852.90		$	4,057.70
Assets that are financed with capital lease obligations	The following table shows assets we financed with capital lease obligations as of December 31 (in millions):
		2014			2013
	Marine vessels	$	83.1		$	81.4
	Less: allowance for depreciation	(75.3		)	(71.4		)
		$	7.8		$	10
Future minimum rental payments due under noncancelable operating leases	uture contractual rental payments due under noncancelable leases as of December 31, 2014 (in millions):
		Capital			Recourse			Nonrecourse
		Leases			Operating			Operating
					Leases			Leases (1)
	2015	$	3.1		$	86.3		$	11
	2016	2.7			89			8.1
	2017	1.1			94.2			9.5
	2018	—			85.6			9
	2019	—			81.5			9.7
	Years thereafter	—			310.1			18.7
		$	6.9		$	746.7		$	66
	Less: amounts representing interest	(0.6		)
	Present value of future contractual capital lease payments	$	6.3
	__________
	(1) The amounts shown are primarily the rental payments of one wholly owned, bankruptcy-remote special purpose corporations. We consolidate these rentals for accounting purposes, but they are not our legal obligations.

Investments_in_Affiliated_Comp1

Investments in Affiliated Companies (Tables)	12 Months Ended
	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Significant Investments in Affiliated Companies, by Segment	The following table presents our most significant investments in affiliated companies and our ownership percentage in those companies by segment as of December 31, 2014 (in millions):
		Segment		Investment				Percentage
								Ownership
	Rolls-Royce & Partners Finance (1)	Portfolio Management		$	293.6			50	%
	Cardinal Marine Investments LLC	Portfolio Management		45.1				50	%
	Adler Funding LLC	Rail North America		16.9				12.5	%
	Other affiliates	Various		2.1				Various
	Investments in Affiliated Companies			$	357.7
	__________
	(1) Combined investment balances of fourteen separate joint ventures (collectively, the "RRPF affiliates")
Equity Method Investments, Earnings by Segment	The following table shows our share of affiliates’ earnings by segment for the years ending December 31 (in millions):
		2014				2013				2012
	Rail North America	$	7.9			$	10.3			$	6.5
	Rail International	(0.3		)		21.1				(18.3		)
	Portfolio Management	60.2				60.9				33.4
	Share of affiliates' earnings (pretax)	67.8				92.3				21.6
	Income taxes	(18.3		)		(16.5		)		(2.0		)
	Share of Affiliates' Earnings	$	49.5			$	75.8			$	19.6
Equity method Investments, Investments and Distributions	The following table shows our cash investments in and distributions from our affiliates by segment for the years ended December 31 (in millions):
		Cash Investments											Cash Distributions (1)
		2014				2013				2012			2014		2013		2012
	Rail North America	$	—			$	—			$	—		$	20	$	—	$	14.9
	Rail International	—				—				—			—		—		—
	Portfolio Management	15.3				101.3				29.7			34.2		47		38.3
		$	15.3			$	101.3			$	29.7		$	54.2	$	47	$	53.2
Equity Method Investments, Guarantees	Investments in affiliated companies represent investments in and loans to domestic and foreign affiliates, and primarily include companies offering lease financing and related services for customers operating rail and marine assets, as well as companies that lease aircraft engines. Loan amounts included in investments in affiliated companies were $16.3 million as of December 31, 2014 and $24.2 million as of December 31, 2013.
	In 2014, we sold our investments in the Intermodal Investment Fund V and Intermodal Investment Fund VII affiliates. As a result of these sales, we received aggregate cash proceeds of $18.3 million.
	In 2013, we dissolved our Singco and Somargas marine affiliates, taking direct ownership of five liquefied gas carrying vessels with a fair value of $151.8 million. In connection with the dissolution we paid $101.3 million, primarily to satisfy our share of the affiliates' external debt, and recognized a pretax gain of $2.5 million, which is recorded in share of affiliates' earnings. The vessels continue to operate in a vessel pooling arrangement that our former partner manages.
	In 2013, we sold our 37.5% interest in AAE to our partner, Ahaus Alstätter Eisenbahn Holding AG (“AAE Holding”), and recognized a pretax gain of $9.3 million, which we reported as part of our share of affiliates' earnings. The sale price of $114.1 million consisted of a cash payment at closing of $23.0 million and a seller loan of €67.5 million ($91.1 million) at a market interest rate. The loan was paid in full in January 2015.
	In 2012, our gas compression equipment leasing affiliate, Enerven Compression, LLC ("Enerven"), sold substantially all of its assets and is in the process of liquidating. In connection with the disposition, we recognized an impairment loss of $14.8 million in 2012, which we recorded in our share of affiliates' earnings. In 2013, we reversed $1.1 million of the prior impairment loss due to higher than expected proceeds from the asset sales.
	The following table presents our most significant investments in affiliated companies and our ownership percentage in those companies by segment as of December 31, 2014 (in millions):
		Segment		Investment				Percentage
								Ownership
	Rolls-Royce & Partners Finance (1)	Portfolio Management		$	293.6			50	%
	Cardinal Marine Investments LLC	Portfolio Management		45.1				50	%
	Adler Funding LLC	Rail North America		16.9				12.5	%
	Other affiliates	Various		2.1				Various
	Investments in Affiliated Companies			$	357.7
	__________
	(1) Combined investment balances of fourteen separate joint ventures (collectively, the "RRPF affiliates").
	The following table shows our share of affiliates’ earnings by segment for the years ending December 31 (in millions):
		2014				2013				2012
	Rail North America	$	7.9			$	10.3			$	6.5
	Rail International	(0.3		)		21.1				(18.3		)
	Portfolio Management	60.2				60.9				33.4
	Share of affiliates' earnings (pretax)	67.8				92.3				21.6
	Income taxes	(18.3		)		(16.5		)		(2.0		)
	Share of Affiliates' Earnings	$	49.5			$	75.8			$	19.6
	The following table shows our cash investments in and distributions from our affiliates by segment for the years ended December 31 (in millions):
		Cash Investments											Cash Distributions (1)
		2014				2013				2012			2014		2013		2012
	Rail North America	$	—			$	—			$	—		$	20	$	—	$	14.9
	Rail International	—				—				—			—		—		—
	Portfolio Management	15.3				101.3				29.7			34.2		47		38.3
		$	15.3			$	101.3			$	29.7		$	54.2	$	47	$	53.2
	__________
	-1	Cash distributions exclude proceeds from sales of affiliates of $19.4 million in 2014, $55.6 million in 2013, and $12.5 million in 2012.
	Summarized Financial Data of Affiliates
	The following table shows the aggregated operating results for the years ended December 31 for the affiliated companies we held at December 31 (in millions):
		2014				2013				2012
	Revenues	$	339			$	334.5			$	651.8
	Gains on sales of assets	33.7				43.5				57.4
	Net income	99.6				108.6				75.3
	The following table shows aggregated summarized balance sheet data for our affiliated companies as of December 31 (in millions):
		2014				2013
	Current assets	$	211.6			$	200.5
	Noncurrent assets	3,195.10				2,989.20
	Total assets	$	3,406.70			$	3,189.70
	Current liabilities	$	378.4			$	159.6
	Noncurrent liabilities	2,388.20				2,408.80
	Shareholders’ equity	640.1				621.3
	Total liabilities and shareholders' equity	$	3,406.70			$	3,189.70
	Summarized Financial Data for the RRPF Affiliates
	As noted above, our affiliate investments include 50% interests in each of the RRPF affiliates, a collection of fourteen domestic and foreign joint ventures with Rolls-Royce plc (or affiliates thereof, collectively “Rolls-Royce”), a leading manufacturer of commercial aircraft jet engines. The RRPF affiliates are primarily engaged in two business activities: lease financing of aircraft engines to a diverse group of commercial aircraft operators worldwide and lease financing of aircraft engines to Rolls-Royce for use in their engine maintenance programs. In aggregate, the RRPF affiliates own 433 aircraft engines at December 31, 2014 which are generally depreciated over a useful life of 25 years to an estimated residual value. Lease terms vary but typically range from 7 to 10 years. Rolls-Royce manages each of the RRPF affiliates and also performs substantially all required maintenance activities. Our share of affiliates' earnings (after-tax) from the RRPF affiliates was $42.2 million in 2014, $46.5 million in 2013, and $36.7 million in 2012.
	We derived the following financial information from the combined financial statements of the RRPF affiliates.
	The following table shows condensed income statements of the RRPF affiliates for the years ending December 31 (in millions):
		2014				2013				2012
	Lease revenue from third parties	$	176.9			$	147.6			$	140.4
	Lease revenue from Rolls-Royce	124.7				119.7				112.9
	Depreciation expense	(140.7		)		(120.2		)		(115.1		)
	Interest expense	(59.5		)		(65.8		)		(64.8		)
	Other expenses	(11.8		)		(10.2		)		(16.3		)
	Gains on sales of assets	22.7				35.2				35.9
	Income before income taxes	112.3				106.3				93
	Income tax provision (benefits) (1)	(17.3		)		0.4				(3.8		)
	Net income	$	95			$	106.7			$	89.2
	_________
	(1) Represents income taxes directly attributable to the RRPF affiliates in the United Kingdom. Several of the RRPF affiliates are flow through entities and income taxes are incurred at the shareholder level. Amounts shown for 2013 and 2012 include tax benefits of approximately $15.2 million and $9.2 million, attributable to statutory rate decreases in the United Kingdom.
	The following table shows the condensed balance sheets of the RRPF affiliates as of December 31 (in millions):
	2014				2013
Current assets	$	146.3			$	151
Noncurrent assets, including operating assets, net of accumulated depreciation of $862.8 and $744.5 (a)	2,988.10				2,619.60
Total assets	$	3,134.40			$	2,770.60
Current liabilities	$	358.5			$	141
Long-term debt	2,012.90				1,963.10
Other liabilities	218.1				212.4
Shareholders’ equity	544.9				454.1
Total liabilities and shareholders' equity	$	3,134.40			$	2,770.60
_________
(a) All operating assets were pledged as collateral for long-term debt obligations.
The following table shows contractual future lease receipts from noncancelable leases of the RRPF affiliates as of December 31, 2014 (in millions):
	Rolls-Royce				Third Parties				Total
2015	$	144.6			$	158.9			$	303.5
2016	129.3				141.8				271.1
2017	109.7				130				239.7
2018	102.4				115.7				218.1
2019	97.1				70.7				167.8
Thereafter	212.3				216.2				428.5
	$	795.4			$	833.3			$	1,628.70
The following table shows maturities of debt obligations of the RRPF affiliates as of December 31, 2014 (in millions):
2015	$	277
2016	323.3
2017	252.2
2018	106.9
2019	426
Thereafter	904.5
Total debt principal (1)	$	2,289.90
_________
(1) All debt obligations are nonrecourse to the shareholders.
Equity Method Investments, Summarized Financial Data	The following table shows the aggregated operating results for the years ended December 31 for the affiliated companies we held at December 31 (in millions):
		2014				2013				2012
	Revenues	$	339			$	334.5			$	651.8
	Gains on sales of assets	33.7				43.5				57.4
	Net income	99.6				108.6				75.3
	The following table shows aggregated summarized balance sheet data for our affiliated companies as of December 31 (in millions):
		2014				2013
	Current assets	$	211.6			$	200.5
	Noncurrent assets	3,195.10				2,989.20
	Total assets	$	3,406.70			$	3,189.70
	Current liabilities	$	378.4			$	159.6
	Noncurrent liabilities	2,388.20				2,408.80
	Shareholders’ equity	640.1				621.3
	Total liabilities and shareholders' equity	$	3,406.70			$	3,189.70
Schedule of Future Minimum Lease Payments Receivable	The following table shows our future contractual receipts from finance leases and noncancelable operating leases as of December 31, 2014 (in millions):
		Finance Leases				Operating Leases (1)				Total
	2015	$	26.3			$	923.4			$	949.7
	2016	25.2				740.3				765.5
	2017	23.9				584.1				608
	2018	22.2				464.7				486.9
	2019	11.8				370				381.8
	Years thereafter	95.4				770.4				865.8
		$	204.8			$	3,852.90			$	4,057.70
Schedule of Maturities of Debt Obligations	The following table shows the scheduled principal payments of our debt obligations as of December 31, 2014 (in millions):
	2015	$	529.2
	2016	639.2
	2017	455.4
	2018	507.5
	2019	592.3
	Thereafter	1,480.20
	Total debt principal	$	4,203.80
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments, Summarized Financial Data	The following table shows condensed income statements of the RRPF affiliates for the years ending December 31 (in millions):
		2014				2013				2012
	Lease revenue from third parties	$	176.9			$	147.6			$	140.4
	Lease revenue from Rolls-Royce	124.7				119.7				112.9
	Depreciation expense	(140.7		)		(120.2		)		(115.1		)
	Interest expense	(59.5		)		(65.8		)		(64.8		)
	Other expenses	(11.8		)		(10.2		)		(16.3		)
	Gains on sales of assets	22.7				35.2				35.9
	Income before income taxes	112.3				106.3				93
	Income tax provision (benefits) (1)	(17.3		)		0.4				(3.8		)
	Net income	$	95			$	106.7			$	89.2
	_________
	(1) Represents income taxes directly attributable to the RRPF affiliates in the United Kingdom. Several of the RRPF affiliates are flow through entities and income taxes are incurred at the shareholder level. Amounts shown for 2013 and 2012 include tax benefits of approximately $15.2 million and $9.2 million, attributable to statutory rate decreases in the United Kingdom.
	The following table shows the condensed balance sheets of the RRPF affiliates as of December 31 (in millions):
		2014				2013
	Current assets	$	146.3			$	151
	Noncurrent assets, including operating assets, net of accumulated depreciation of $862.8 and $744.5 (a)	2,988.10				2,619.60
	Total assets	$	3,134.40			$	2,770.60
	Current liabilities	$	358.5			$	141
	Long-term debt	2,012.90				1,963.10
	Other liabilities	218.1				212.4
	Shareholders’ equity	544.9				454.1
	Total liabilities and shareholders' equity	$	3,134.40			$	2,770.60
	_________
	(a) All operating assets were pledged as collateral for long-term debt obligations.
Schedule of Future Minimum Lease Payments Receivable	The following table shows contractual future lease receipts from noncancelable leases of the RRPF affiliates as of December 31, 2014 (in millions):
		Rolls-Royce				Third Parties				Total
	2015	$	144.6			$	158.9			$	303.5
	2016	129.3				141.8				271.1
	2017	109.7				130				239.7
	2018	102.4				115.7				218.1
	2019	97.1				70.7				167.8
	Thereafter	212.3				216.2				428.5
		$	795.4			$	833.3			$	1,628.70
Schedule of Maturities of Debt Obligations	The following table shows maturities of debt obligations of the RRPF affiliates as of December 31, 2014 (in millions):
	2015	$	277
	2016	323.3
	2017	252.2
	2018	106.9
	2019	426
	Thereafter	904.5
	Total debt principal (1)	$	2,289.90
	_________
	(1) All debt obligations are nonrecourse to the shareholders

Loans_Tables

Loans (Tables)	12 Months Ended
	Dec. 31, 2014
Loans Receivable, Net [Abstract]
Schedule of Loan Receivables, Minimum Payments	The following table shows scheduled loan principal payments due by year at December 31, 2014 (in millions):
	2015	$	86.4
	2016	4.3
	2017	2
	2018	4.6
	2019	—
	Thereafter	—
		$	97.3

Variable_Interest_Entities_Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2014
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Carrying amounts of assets and liabilities of consolidated VIE	The following table shows the carrying amounts of assets and liabilities of the consolidated variable interest entity as of December 31 (in millions):
		2014		2013
	Operating assets, net of accumulated depreciation (1)	$	88.1	$	93
	Nonrecourse debt	15.9		25.4
	_________
	-1	All operating assets are pledged as collateral on the nonrecourse debt.
Carrying amounts and maximum exposure to loss for non consolidated VIEs	The following table shows the carrying amounts and maximum exposure to loss for our unconsolidated variable interest entities as of December 31 (in millions):
		2014				2013
		Net Carrying Amount		Maximum Exposure to Loss		Net Carrying Amount		Maximum Exposure to Loss
	Investments in affiliates	$	143.9	$	143.9	$	125.5	$	125.5
	Other investment	0.4		0.4		0.6		0.6
	Total	$	144.3	$	144.3	$	126.1	$	126.1

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Commercial Paper and Borrowings Under Bank Credit Facilities	Commercial Paper and Borrowings Under Bank Credit Facilities ($ in millions)
		31-Dec
		2014			2013
	Balance	$	72.1		$	23.6
	Weighted average interest rate	0.56		%	0.8		%
Outstanding balances of debt obligations and the applicable interest rates	utstanding balances of our debt obligations and the applicable interest rates as of December 31 ($ in millions):
		Date of Issue		Final	Interest Rate			2014			2013
				Maturity
	Recourse Fixed Rate Debt
	Unsecured	4/14/05		4/15/15	5.7	%		$	100		$	100
	Unsecured	2/5/10		5/15/15	4.75	%		250			250
	Unsecured	12/22/05		12/22/15	5.75	%		70			85
	Unsecured	3/3/06		3/1/16	5.8	%		200			200
	Unsecured	11/19/10		7/15/16	3.5	%		250			250
	Unsecured	9/20/11		7/15/16	3.5	%		100			100
	Unsecured	3/4/14		3/4/17	1.25	%		300			—
	Unsecured	2/6/08		2/15/18	6	%		200			200
	Unsecured	3/19/13		7/30/18	2.38	%		250			250
	Unsecured (1)	12/27/10		10/31/18	3.84	%		15.7			22
	Unsecured (1)	11/29/10		11/30/18	3.7	%		12.1			17.2
	Unsecured	11/19/13		3/15/19	2.5	%		300			300
	Unsecured	3/4/14		7/30/19	2.5	%		250			—
	Unsecured	10/31/14		3/30/20	2.6	%		250			—
	Unsecured	5/27/11		6/1/21	4.85	%		250			250
	Unsecured	9/20/11		6/1/21	4.85	%		50			50
	Unsecured	6/11/12		6/15/22	4.75	%		250			250
	Unsecured	3/19/13		3/30/23	3.9	%		250			250
	Unsecured	3/4/14		3/15/44	5.2	%		300			—
	Unsecured	4/30/09		5/15/14	8.75	%		—			300
	Total recourse fixed rate debt							$	3,647.80		$	2,874.20
	Recourse Floating Rate Debt
	Unsecured	12/15/10		10/31/15	1.47	%		$	24.8		$	36.4
	Unsecured (1)	12/6/11		8/31/16	1.57	%		15.3			22.1
	Unsecured (1)	9/2/11		8/31/16	1.13	%		8			11.5
	Unsecured (1)	3/29/06		9/30/16	2.08	%		18.9			32.2
	Unsecured (1)	6/29/07		9/30/16	2.03	%		8.5			14.4
	Unsecured (1)	12/18/07		10/31/16	1.98	%		12.7			21.6
	Unsecured	12/21/12		12/21/17	1.39	%		100			100
	Unsecured	1/22/13		12/21/17	1.39	%		10			70
	Unsecured (1)	8/31/12		12/31/19	2.33	%		60.5			68.7
		Date of Issue		Final	Interest Rate			2014			2013
				Maturity
	Unsecured (1)	6/27/13		12/31/20	1.87	%		121			137.5
	Unsecured (1)	10/30/13		12/31/20	1.91	%		30.2			34.4
	Unsecured (1)	5/5/14		12/31/20	1.99	%		30.2			—
	Unsecured	8/28/14		8/28/24	1.54	%		100			—
	Unsecured	3/1/10		2/28/15	1.83	%		—			13.7
	Unsecured	12/12/11		6/12/17	1.63	%		—			103.5
	Unsecured	8/12/13		6/12/17	1.63	%		—			71.1
	Unsecured	1/12/12		6/12/17	1.63	%		—			31.5
	Unsecured	2/21/13		12/21/17	1.81	%		—			35
	Secured	12/19/11		12/19/20	2.1	%		—			91.1
	Total recourse floating rate debt							$	540.1		$	894.7
	Nonrecourse Fixed Rate Debt
	Secured (1)	9/30/97		9/20/16	6.69	%		$	15.9		$	25.4
	Total nonrecourse fixed rate debt							$	15.9		$	25.4
	Nonrecourse Floating Rate Debt
	Secured	Various		5/8/14	1.4	%		$	—		$	47.7
	Total nonrecourse floating rate debt							$	—		$	47.7
	Total debt principal							$	4,203.80		$	3,842.00
	Debt discount, net							(8.6		)	(8.9		)
	Debt adjustment for fair value hedges							0.6			5.4
	Total Debt							$	4,195.80		$	3,838.50
Maturities of GATX's debt obligation	The following table shows the scheduled principal payments of our debt obligations as of December 31, 2014 (in millions):
	2015	$	529.2
	2016	639.2
	2017	455.4
	2018	507.5
	2019	592.3
	Thereafter	1,480.20
	Total debt principal	$	4,203.80

Fair_Value_Disclosure_Tables

Fair Value Disclosure (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Assets and liabilities at fair value recurring basis	The following tables show our assets and liabilities that are measured at fair value on a recurring basis (in millions):
	Assets	Total			Quoted Prices in Active Markets for Identical Assets			Significant Observable Inputs			Significant Unobservable Inputs
		December 31,			(Level 1)			(Level 2)			(Level 3)
		2014
	Interest rate derivatives (1)	$	1.8		$	—		$	1.8		$	—
	Foreign exchange rate derivatives (2)	9.7			—			9.7			—
	Available-for-sale equity securities	4.4			4.4			—			—
	Liabilities
	Interest rate derivatives (1)	5.9			—			5.9			—
	Foreign exchange rate derivatives (2)	1.6			—			1.6			—
	Assets	Total			Quoted Prices in Active Markets for Identical Assets			Significant Observable Inputs			Significant Unobservable Inputs
		December 31,			(Level 1)			(Level 2)			(Level 3)
		2013
	Interest rate derivatives (1)	$	6		$	—		$	6		$	—
	Available-for-sale equity securities	4.7			4.7			—			—
	Liabilities
	Interest rate derivatives (1)	0.8			—			0.8			—
	Interest rate derivatives (2)	0.2			—			0.2			—
	Foreign exchange rate derivatives (2)	2.6			—			2.6			—
	_________
	-1	Designated as hedges.
	-2	Not designated as hedges.
	We base our valuations of available-for-sale equity securities on their quoted prices on an active exchange. We value derivatives using a pricing model with inputs (such as yield curves and credit spreads) that are observable in the market or that can be derived principally from observable market data.
Non-recurring Level 3 fair value measurements	The following table shows disclosures related to our non-recurring Level 3 fair value measurements (in millions):
		Fair Value			Impairment Losses
		of Assets
	2014
	Operating assets (1)	$	2.5		$	0.7
	2013
	Operating assets (1)	9.6			2.5
	2012
	Investment in affiliated companies (2)	32.9			14.8
	Operating assets (1)	0.7			0.7
Impact of GATX's Derivative Instrument On Income Statement and Other comprehensive income (loss)	Derivative instruments
	Fair Value Hedges
	We use interest rate swaps to manage the fixed-to-floating rate mix of our debt obligations by converting the fixed rate debt to floating rate debt. For fair value hedges, we recognize changes in fair value of both the derivative and the hedged item as interest expense. We had eight instruments outstanding with an aggregate notional amount of $600.0 million as of December 31, 2014 and three instrument outstanding with an aggregate notional amount of $200.0 million as of December 31, 2013. These derivatives have maturities ranging from 2015 to 2020.
	Cash Flow Hedges
	We use interest rate swaps to convert floating rate debt to fixed rate debt. We use Treasury rate locks to hedge our exposure to interest rate risk on anticipated transactions. We also use currency swaps to hedge our exposure to fluctuations in the exchange rates of the foreign currencies in which we conduct business. We had seven instruments outstanding with an aggregate notional amount of $281.5 million as of December 31, 2014 and six instruments outstanding with an aggregate notional amount of $163.6 million as of December 31, 2013. These derivatives had maturities ranging from 2015 to 2020. Within the next 12 months, we expect to reclassify $6.0 million ($3.8 million after-tax) of net losses on previously terminated derivatives from accumulated other comprehensive income (loss). We reclassify these amounts when interest and operating lease expense on the related hedged transactions affect earnings.
	Non-designated Derivatives
	We do not hold derivative financial instruments for purposes other than hedging, although certain of our derivatives are not designated as accounting hedges. We recognize changes in the fair value of these derivatives in other (income) expense immediately.
	Some of our derivative instruments contain credit risk provisions that could require us to make immediate payment on net liability positions in the event that we default on certain outstanding debt obligations. The aggregate fair value of our derivative instruments with credit risk related contingent features that are in a liability position as of December 31, 2014 was $5.9 million. We are not required to post any collateral on our derivative instruments and do not expect the credit risk provisions to be triggered.
	In the event that a counterparty fails to meet the terms of an interest rate swap agreement or a foreign exchange contract, our exposure is limited to the fair value of the swap, if in our favor. We manage the credit risk of counterparties by transacting with institutions that we consider financially sound and by avoiding concentrations of risk with a single counterparty. We believe that the risk of non-performance by any of our counterparties is remote.
	The following table shows the impacts of our derivative instruments on our statement of comprehensive income for the years ended December 31 (in millions):
	Derivative Designation		Location of Loss (Gain) Recognized	2014			2013			2012
	Fair value hedges (1)		Interest expense	$	4.7		$	4.9		$	5
	Cash flow hedges		Other comprehensive loss (effective portion)	5.1			(0.7		)	0.2
	Cash flow hedges		Interest expense (effective portion reclassified from accumulated other comprehensive loss)	4.9			5.1			4.2
	Cash flow hedges		Operating lease expense (effective portion reclassified from accumulated other comprehensive loss)	3.2			1.5			1.4
	Cash flow hedges		Other (income) expense (effective portion reclassified from accumulated other comprehensive loss)	(2.1		)	—			—
	Cash flow hedges		Other (income) expense (ineffective portion)	—			—			(0.1		)
	Non-designated (2)		Other (income) expense	(11.4		)	(0.6		)	5
	_________
	-1	The fair value adjustments related to the underlying debt equally offset the amounts recognized in interest expense.
	-2	For 2014, includes $10.4 million of gains on foreign currency derivatives which substantially offset losses from foreign currency remeasurement adjustments on the AAE loan, also recognized in other income.
Fair Value Other Financial Instruments	The following table shows the carrying amounts and fair values of our other financial instruments as of December 31 (in millions):
		2014			2014			2013			2013
		Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value
	Assets
	Investment funds	$	1.5		$	2.4		$	1.7		$	4
	Loans	97.3			97.4			122.7			121.5
	Liabilities
	Recourse fixed rate debt	$	3,639.90		$	3,775.00		$	2,871.20		$	2,994.00
	Recourse floating rate debt	540			540			894.7			906.2
	Nonrecourse debt	15.9			16.6			72.6			74.7

Pension_and_Other_PostRetireme1

Pension and Other Post-Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension obligations and plan assets and other post-retirement obligations	We use a December 31 measurement date for all of our plans. The following tables show pension obligations, plan assets, and other post-retirement obligations as of December 31 (in millions):
		2014 Pension				2013 Pension				2014 Retiree			2013 Retiree
		Benefits				Benefits				Health			Health
										and Life			and Life
	Change in Benefit Obligation
	Benefit obligation at beginning of year	$	442.7			$	473.8			$	40.4		$	48.1
	Service cost	5.9				6.7				0.1			0.2
	Interest cost	20.7				18.4				1.6			1.6
	Actuarial loss (gain)	67				(26.8		)		2.6			(6.2		)
	Benefits paid	(31.2		)		(30.3		)		(3.9		)	(3.3		)
	Effect of foreign exchange rate changes	(2.4		)		0.9				—			—
	Benefit obligation at end of year	$	502.7			$	442.7			$	40.8		$	40.4
	Change in Fair Value of Plan Assets
	Plan assets at beginning of year	447.8				409.1				—			—
	Actual return on plan assets	40.3				65.9				—			—
	Effect of exchange rate changes	(2.4		)		0.7				—			—
	Company contributions	2.4				2.4				3.9			3.3
	Benefits paid	(31.2		)		(30.3		)		(3.9		)	(3.3		)
	Plan assets at end of year	$	456.9			$	447.8			$	—		$	—
	Funded Status at end of year	$	(45.8	)		$	5.1			$	(40.8	)	$	(40.4	)
	Amount Recognized
	Other liabilities (assets), net	$	(45.8	)		$	5.1			$	(40.8	)	$	(40.4	)
	Accumulative other comprehensive loss:
	Net actuarial loss	170.9				127.6				3.3			0.6
	Prior service (credit) cost	(2.1		)		(3.1		)		0.4			0.4
	Accumulated other comprehensive loss	168.8				124.5				3.7			1
	Total recognized	$	123.2			$	129.6			$	(37.1	)	$	(39.4	)
	After-tax amount recognized in accumulated other comprehensive loss	$	105.4			$	77.6			$	2.3		$	0.6
	The aggregate accumulated benefit obligation for the defined benefit pension plans was $475.8 million at December 31, 2014 and $426.3 million at December 31, 2013.
Pension plans with a projected benefit obligation in excess of plan assets	The following table shows our pension plans that have a projected benefit obligation in excess of plan assets as of December 31 (in millions):
		2014				2013
	Projected benefit obligations	$	502.7			$	67.8
	Fair value of plan assets	456.9				40
Pension plans with an accumulated benefit obligation in excess of plan assets	The following table shows our pension plans that have an accumulated benefit obligation in excess of plan assets as of December 31 (in millions):
		2014				2013
	Accumulated benefit obligations	$	170.6			$	66.4
	Fair value of plan assets	140.5				40
Components of pension and other post retirement benefit costs	The following table shows the components of net periodic cost (benefit) for the year ended December 31 (in millions):
		2014				2013				2012			2014			2013			2012
		Pension				Pension				Pension			Retiree Health and Life			Retiree Health and Life			Retiree Health and Life
		Benefits				Benefits				Benefits
	Service cost	$	5.9			$	6.7			$	5.7		$	0.1		$	0.2		$	0.2
	Interest cost	20.7				18.4				19.7			1.6			1.6			2
	Expected return on plan assets	(28.4		)		(27.5		)		(29.6		)	—			—			—
	Amortization of:
	Unrecognized prior service credit	(1.0		)		(1.0		)		(1.0		)	(0.1		)	(0.1		)	(0.1		)
	Unrecognized net actuarial loss (gain)	11.3				14.9				9.9			(0.1		)	—			(0.1		)
	Net periodic cost	$	8.5			$	11.5			$	4.7		$	1.5		$	1.7		$	2
Schedule of amounts in accumulated other comprehensive loss (gain) to be recognized over next fiscal year	We amortize the unrecognized prior service credit using a straight-line method over the average remaining service period of the employees we expect to receive benefits under the plan. We amortize the unrecognized net actuarial loss (gain), which is subject to certain averaging conventions, over the average remaining service period of active employees.
	The following table shows the amounts we expect to recognize as components of net periodic cost in 2015 from amounts recorded in accumulated comprehensive loss (gain) as of December 31, 2014 (in millions):
		2015
		Pension Benefits				Retiree Health and Life
	Unrecognized net actuarial loss	$	14.1			$	0.1
	Unrecognized prior service credit (cost)	(1.0		)		0.1
Expected long term return on assets and to measure the periodic cost	We use the following assumptions to measure the benefit obligation, compute the expected long-term return on assets, and measure the periodic cost for our defined benefit pension plans and other post-retirement benefit plans for the years ended December 31:
		2014			2013
	Domestic defined benefit pension plans
	Benefit Obligation at December 31:
	Discount rate — salaried funded and unfunded plans	4.05	%		4.8	%
	Discount rate — hourly funded plan	4.1	%		4.9	%
	Rate of compensation increases — salaried funded and unfunded plans	2.5	%		3	%
	Rate of compensation increases — hourly funded plans	N/A			N/A
	Net Periodic Cost (Benefit) for the years ended December 31:
	Discount rate — salaried funded and unfunded plans	4.8	%		3.95	%
	Discount rate — hourly funded plan	4.9	%		4.05	%
	Expected return on plan assets — salaried funded plan	7.6	%		7.75	%
	Expected return on plan assets — hourly funded plan	6.9	%		6.8	%
	Rate of compensation increases — salaried funded and unfunded plans	3	%		3	%
	Rate of compensation increases — hourly funded plan	N/A			N/A
	Foreign defined benefit pension plan
	Benefit Obligation at December 31:
	Discount rate	3.2	%		4.4	%
	Rate of pension-in-payment increases	2.9	%		3.4	%
	Net Periodic Cost (Benefit) for the years ended December 31:
	Discount rate	4.4	%		4.25	%
	Expected return on plan assets	5.4	%		5.34	%
	Rate of pension-in-payment increases	3.4	%		3	%
	Other post-retirement benefit plans
	Benefit Obligation at December 31:
	Discount rate - salaried health	3.65	%		4.2	%
	Discount rate - hourly health	3.85	%		4.6	%
	Discount rate - salaried life insurance	4	%		4.75	%
	Discount rate - hourly life insurance	3.7	%		4.4	%
	Rate of compensation increases	N/A			N/A
	Net Periodic Cost (Benefit) for the years ended December 31:
	Discount rate - salaried health	4.2	%		3.65	%
	Discount rate - hourly health	4.6	%		3.6	%
	Discount rate - salaried life insurance	4.75	%		3.9	%
	Discount rate - hourly life insurance	4.4	%		3.45	%
	Rate of compensation increases	N/A			N/A
Review of historical returns	We calculate the present value of expected future pension and post-retirement cash flows as of the measurement date using a discount rate. We base the discount rate on yields for high-quality, long-term bonds with durations similar to that of our projected benefit obligation. We base the expected return on our plan assets on current and expected asset allocations, as well as historical and expected returns on various categories of plan assets. We routinely review our historical returns along with current market conditions to ensure our expected return assumption is reasonable and appropriate.
		2014			2013
	Assumed Health Care Cost Trend Rates at December 31
	Health care cost trend assumed for next year
	Medical claims	7.5	%		8	%
	Prescription drugs claims	7	%		7	%
	Rate to which the cost trend is expected to decline (the ultimate trend rate)
	Medical claims	5	%		5	%
	Prescription drugs claims	5	%		5	%
	Year that rate reaches the ultimate trend rate
	Medical claims	2023			2020
	Prescription drugs claims	2023			2020
Effect on the other post-retirement benefit cost and obligation	The health care cost trend, which is based on projected growth rates for medical and prescription drug claims, has a significant effect on our other post-retirement benefit costs and obligations. The following table shows the effects of a one percentage point change in the health care cost trend rate on service and interest costs for the year ended December 31, 2014 and the post-retirement benefit obligation as of December 31, 2014 (in millions) :
		One Percentage Point				One Percentage Point
		Increase				Decrease
	Effect on total of service and interest cost	$	0.1			$	(0.1	)
	Effect on post-retirement benefit obligation	2.6				(2.3		)
Pension plan assets fair value	The following tables set forth the fair value of our pension plan assets as of December 31 (in millions):
		Total				Quoted Prices in Active Markets for Identical Assets				Significant Observable Inputs			Significant Unobservable Inputs (Level 3)
		December 31,				(Level 1)				(Level 2)
		2014
	Assets
	Short-term investment funds	$	0.9			$	0.9			$	—		$	—
	Common stock												—
	US equities	13.3				13.3				—			—
	International equities	1.6				1.6				—			—
	Common stock collective funds	215.2				—				215.2			—
	Fixed income collective trust funds	208.1				—				208.1			—
	Real estate collective trust funds	17.9				—				17.9			—
	Total	$	457			$	15.8			$	441.2		$	—
		Total				Quoted Prices in Active Markets for Identical Assets				Significant Observable Inputs			Significant Unobservable Inputs (Level 3)
		December 31,				(Level 1)				(Level 2)
		2013
	Assets
	Short-term investment funds	$	1.3			$	1.3			$	—		$	—
	Common stock												—
	US equities	21.4				21.4				—			—
	International equities	2.4				2.4				—			—
	Common stock collective funds	263				—				263			—
	Fixed income collective trust funds	138				—				138			—
	Real estate collective trust funds	21.7				—				21.7			—
	Total	$	447.8			$	25.1			$	422.7		$	—
Schedule of Expected Benefit Payments	The following table shows benefit payments, which reflect expected future service, as appropriate, we expect the plan to pay (in millions):
		Funded Plans				Unfunded Plans				Retiree Health and Life
	2015	$	28.2			$	2			$	3.5
	2016	28.3				2.2				3.4
	2017	28.7				2.3				3.3
	2018	29.2				2.3				3.2
	2019	29.6				2.8				3.1
	Years 2020-2024	152.2				15.3				14
		$	296.2			$	26.9			$	30.5
Contributions to Multiemployer Benefit Plans	The following table shows our contributions to multiemployer benefit plans for the years indicated (in millions):
	Multiemployer Plans		EIN and Pension Plan Number		Pension Protection Act Zone Status		GATX Contributions										Collective Bargaining Agreement Expiration Date
							2014				2013			2012
	American Maritime Officers Pension Plan (1)		13-1969709-001		Endangered-Yellow		$	1.5			$	1.4		$	1.5		January 15, 2017
	Other multiemployer post-retirement plans						7				6.7			6.6
	Total						$	8.5			$	8.1		$	8.1
	__________________
	(1)Our contributions represented more than 5% of the total contributions to the plan during each year and no surcharge was imposed for any year. The actuary for the American Maritime Officers Pension Plan certified that the plan is in endangered status (i.e. “yellow zone” as defined by the Pension Protection Act of 2006) for the plan year beginning October 1, 2013, because it has funding or liquidity problems, or both. A rehabilitation plan, as defined by the Employee Retirement Security Act of 1974, was instituted under which certain adjustable benefits were reduced or eliminated, and we are required to contribute at a negotiated rate per day worked by each employee.
Foreign Funded Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocations of domestic funded pension plans	The following table shows the weighted-average asset allocations of our foreign funded pension plan at December 31, 2014 and 2013, and current target asset allocation for 2015, by asset category:
					Plan Assets at
					31-Dec
		Target			2014			2013
	Asset Category
	Equity securities	36.8	%		37.7	%		38.5	%
	Debt securities	63.2	%		62.3	%		61.5	%
		100	%		100	%		100	%
Domestic defined benefit pension plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted-average asset allocations of domestic funded pension plans	Our investment policies require that asset allocations of domestic and foreign funded pension plans be maintained at certain targets. The following table shows our weighted-average asset allocations of our domestic funded pension plans at December 31, 2014 and 2013, and current target asset allocation for 2015, by asset category:
					Plan Assets at
					31-Dec
		Target			2014			2013
	Asset Category
	Equity securities	52	%		51.7	%		66.7	%
	Debt securities	44	%		43.9	%		27.8	%
	Real estate	4	%		4.3	%		5.4	%
	Cash	—	%		0.1	%		0.1	%
		100	%		100	%		100	%

Share_Based_Compensation_Table

Share Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted Average Fair Value and Assumptions	The following table shows the weighted average fair value for our stock appreciation rights and the assumptions we used to estimate fair value:
		2014				2013			2012
	Weighted average estimated fair value	$	18.12			$	18.89		$	18.48
	Quarterly dividend rate	$	0.33			$	0.3		$	0.29
	Expected term of stock appreciation rights, in years	4.4				4.7			4.7
	Risk-free interest rate	1.3		%		0.7		%	1		%
	Dividend yield	2.3		%		2.6		%	2.7		%
	Expected stock price volatility	30.3		%		42.4		%	43.3		%
	Present value of dividends	$	5.76			$	5.6		$	5.37
Data With Respect to Stock Options SARs Activity	The following table shows information about outstanding stock options and stock appreciation rights for the year ended December 31, 2014:
		Number of Stock Options and Stock Appreciation Rights		Weighted Average Exercise Price
		(in thousands)
	Outstanding at beginning of the year	1,694		$	36.03
	Granted	297		58.5
	Exercised	-467		37.71
	Forfeited/Cancelled	-33		50.71
	Expired	-1		41.02
	Outstanding at end of the year	1,490		39.65
	Vested and exercisable at end of the year	919		32.08
Schedule of Share-Based Compensation, Aggregate Intrinsic Value and Weighted Average Remaining Contractual Term	The following table shows the aggregate intrinsic value of stock options and stock appreciation rights exercised in 2014, 2013, and 2012, and the weighted average remaining contractual term and aggregate intrinsic value of stock appreciation rights outstanding and vested as of December 31, 2014:
	Stock Options and Stock Appreciation Rights	Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
		(Years)		(in millions)
	Exercised in 2012			$	4.9
	Exercised in 2013			6.9
	Exercised in 2014			11.8
	Outstanding at December 31, 2014 (a)	3.7		27.5
	Vested and exercisable at December 31, 2014	2.6		23.8
	__________________
	(a) As of December 31, 2014, there are no remaining stock options outstanding.
Schedule of Share-Based Compensation, Restricted Stock Units and Performance Shares Award Activity	The following table shows information about restricted stock units and performance shares for the year ended December 31, 2014:
		Number of Share Units Outstanding			Weighted Average Grant-Date Fair Value
	Restricted Stock Units:
	Nonvested at beginning of the year	200,050			$	41.17
	Granted	56,020			58.66
	Vested	(70,986	)		34.77
	Forfeited	(7,874	)		49.42
	Nonvested at end of the year	177,210			48.9
	Performance Shares:
	Nonvested at beginning of the year	160,332			$	44.48
	Granted	62,670			53.63
	Net increase due to estimated performance	67,392			47.49
	Vested	(92,958	)		44.02
	Forfeited	(22,367	)		46.57
	Nonvested at end of the year	175,069			48.95

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Components of Deferred tax Assets and Liabilities	significant components of our deferred tax liabilities and assets as of December 31 (in millions):
		2014			2013
	Deferred Tax Liabilities
	Book/tax basis difference due to depreciation	$	963.8		$	852
	Investments in affiliated companies	99.7			93.7
	Lease accounting	10.5			24.4
	Other	0.1			—
	Total deferred tax liabilities	1,074.10			970.1
	Deferred Tax Assets
	Federal net operating loss	41.8			8.9
	Alternative minimum tax credit	9.2			8.4
	Foreign tax credit	3.6			3.6
	Valuation allowance on foreign tax credit	(3.6		)	(3.6		)
	State net operating loss	28.7			27.1
	Valuation allowance on state net operating loss	(11.3		)	(11.2		)
	Foreign net operating loss	5.8			8.5
	Valuation allowance on foreign net operating loss	(0.2		)	(0.2		)
	Accruals not currently deductible for tax purposes	18.7			14.1
	Allowance for losses	1.7			2.2
	Pension and post-retirement benefits	32.6			13.3
	Other	9.8			7.6
	Total deferred tax assets	136.8			78.7
	Net deferred tax liabilities	937.3			$	891.4
Gross liability for unrecognized tax benefits	The following table shows a reconciliation of the beginning and ending amount of our gross liability for unrecognized tax benefits (in millions)
		2014			2013
	Beginning balance	$	5.7		$	4.7
	Reductions due to settlement of tax audit issues	(0.4		)	—
	Additions to tax positions for prior years	0.3			1
	Ending balance	$	5.6		$	5.7
Income before income taxes	The following table shows the components of income before income taxes, excluding affiliates, for the years ending December 31 (in millions):
		2014			2013			2012
	Domestic	$	137.9		$	66		$	80.5
	Foreign	93.3			93			63.3
		$	231.2		$	159		$	143.8
Consolidated federal income taxes	The following table shows income taxes, excluding domestic and foreign joint ventures, for the years ending December 31 (in millions):
		2014			2013			2012
	Current
	Domestic:
	Federal	$	0.7		$	1.4		$	(8.8	)
	State and local	0.6			—			2.5
		1.3			1.4			(6.3		)
	Foreign	13			10.5			8
		14.3			11.9			1.7
	Deferred
	Domestic:
	Federal	45			36.6			16
	State and local	5.6			5.3			(3.1		)
		50.6			41.9			12.9
	Foreign	10.8			11.7			11.5
		61.4			53.6			24.4
	Income taxes	$	75.7		$	65.5		$	26.1
Summary of reasons for difference between GATX's effective income tax rate and federal statutory income tax	The following table shows the differences between our effective income tax rate and the federal statutory income tax rate for the years ending December 31 (in millions):
		2014			2013			2012
	Income taxes at federal statutory rate	$	80.9		$	55.6		$	50.4
	Adjust for effect of:
	GATX income taxes on sale of AAE	—			23.2			—
	Foreign tax credits	—			(3.9		)	(13.7		)
	Foreign earnings taxed at lower rates	(8.5		)	(10.3		)	(4.1		)
	Tax effect of foreign dividends	—			—			6.3
	Expiration of the applicable statute of limitations	—			—			(15.5		)
	Corporate owned life insurance	(0.6		)	(0.5		)	(0.3		)
	State income taxes	4.1			1.5			1.9
	Other	(0.2		)	(0.1		)	1.1
	Income taxes	$	75.7		$	65.5		$	26.1
	Effective income tax rate	32.7		%	41.2		%	18.2		%

Commercial_Commitments_Tables

Commercial Commitments (Tables)	12 Months Ended
	Dec. 31, 2013
Guarantees [Abstract]
Commercial Commitments	The following table shows our commercial commitments as of December 31 (in millions):
		2014		2013
	Lease payment guarantees	$	28.5	$	34.8
	Standby letters of credit	8.7		8.8
	Performance bonds	0.4		0.6
	Asset residual value guarantees	—		5.6
	Total commercial commitments (1)	$	37.6	$	49.8
	__________________
	-1	The carrying value of liabilities on the balance sheet for commercial commitments was $5.1 million at December 31, 2014 and $6.2 million at December 31, 2013. The expirations of these commitments range from 2017 to 2023. We are not aware of any event that would require us to satisfy any of our commitments.

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Computation of basic and diluted net income per common share	The following table shows the computation of our basic and diluted net income per common share for the years ending December 31 (in millions, except per share amounts):
		2014		2013		2012
	Numerator:
	Net income	$	205	$	169.3	$	137.3
	Denominator:
	Denominator for basic earnings per share — weighted average shares	45		46.4		46.8
	Effect of dilutive securities
	Equity compensation plans	0.8		0.7		0.7
	Convertible preferred stock	—		—		0.1
	Weighted average shares outstanding - diluted	45.8		47.1		47.6
	Basic earnings per share	$	4.55	$	3.64	$	2.93
	Diluted earnings per share	$	4.48	$	3.59	$	2.88

Allowance_for_Losses_Tables

Allowance for Losses (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Changes in the allowance for possible losses	The following table shows changes in the allowance for losses at December 31 (in millions):
		2014			2013
	Beginning balance	$	5.2		$	4.6
	Provision for losses	0.8			0.7
	Charges to allowance	(0.3		)	—
	Recoveries and other, including foreign exchange adjustments	—			(0.1		)
	Ending balance	$	5.7		$	5.2

Shareholders_Equity_Tables

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Common stock reserved for conversion and incentive plans	The following shares of common stock were reserved as of December 31, 2014 (in millions):
	GATX Corporation 2004 Equity Incentive Compensation Plan	2.5
	GATX Corporation 2012 Incentive Award Plan	3.5
		6

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Accumulated other comprehensive income (loss)	The following table shows the change in components for accumulated other comprehensive loss (in millions):
		Foreign Currency Translation Gain (Loss)			Unrealized Gain (Loss) on Securities			Unrealized Loss on Derivative Instruments			Post-Retirement Benefit Plans			Total
	Balance at December 31, 2011	$	6.4		$	(0.6	)	$	(56.2	)	$	(118.7	)	$	(169.1	)
	Change in component	25			0.5			6.2			(28.8		)	2.9
	Reclassification adjustments into earnings	—			(0.4		)	6.5			8.7			14.8
	Income tax effect	—			0.1			(1.0		)	7.7			6.8
	Balance at December 31, 2012	31.4			(0.4		)	(44.5		)	(131.1		)	(144.6		)
	Change in component	25.8			1.4			22.3			71			120.5
	Reclassification adjustments into earnings	—			—			6.6			13.8			20.4
	Income tax effect	—			(0.6		)	(6.5		)	(31.9		)	(39.0		)
	Balance at December 31, 2013	57.2			0.4			(22.1		)	(78.2		)	(42.7		)
	Change in component	(79.1		)	(0.2		)	0.3			(57.3		)	(136.3		)
	Reclassification adjustments into earnings	—			—			6			10.1			16.1
	Income tax effect	—			0.1			(3.3		)	17.7			14.5
	Balance at December 31, 2014	$	(21.9	)	$	0.3		$	(19.1	)	$	(107.7	)	$	(148.4	)

Foreign_Operations_Tables

Foreign Operations (Tables)	12 Months Ended
	Dec. 31, 2014
Concentration Risks, Types, No Concentration Percentage [Abstract]
Foreign operations data	The following table shows our domestic and foreign revenues and identifiable assets for the years ending or as of December 31 (in millions):
		2014		2013		2012
	Revenues
	Foreign	$	346.2	$	332.1	$	279.8
	United States	1,104.80		988.9		963.4
		$	1,451.00	$	1,321.00	$	1,243.20
	Identifiable Assets
	Foreign	$	2,133.90	$	2,200.10	$	1,897.90
	United States	4,803.60		4,349.50		4,157.50
		$	6,937.50	$	6,549.60	$	6,055.40

Financial_Data_of_Business_Seg1

Financial Data of Business Segments (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Segment data	The following tables show certain segment data for the years ended December 31, 2014, 2013, and 2012 (in millions):
		Rail North America			Rail International			ASC			Portfolio Management			Other			GATX Consolidated
	2014 Profitability
	Revenues
	Lease revenue	$	864.1		$	188.6		$	4.2		$	29.7		$	—		$	1,086.60
	Marine operating revenue	—			—			223			63.3			—			286.3
	Other revenue	63.4			10.3			—			4.4			—			78.1
	Total Revenues	927.5			198.9			227.2			97.4			—			1,451.00
	Expenses
	Maintenance expense	265.5			45.9			25.6			—			—			337
	Marine operating expense	—			—			149.2			48.6			—			197.8
	Depreciation expense	190			47.1			13.6			22.8			—			273.5
	Operating lease expense	103.7			—			5.2			—			(0.2		)	108.7
	Other operating expense	21.9			5.1			—			1.9			—			28.9
	Total Expenses	581.1			98.1			193.6			73.3			(0.2		)	945.9
	Other Income (Expense)
	Net gain (loss) on asset dispositions	72.3			6			(0.5		)	9.4			—			87.2
	Interest expense, net	(98.4		)	(24.7		)	(5.6		)	(24.3		)	(5.4		)	(158.4		)
	Other expense	(7.2		)	(3.1		)	(0.2		)	(1.2		)	(1.8		)	(13.5		)
	Share of affiliates' earnings (pretax)	7.9			(0.3		)	—			60.2			—			67.8
	Segment profit (loss)	$	321		$	78.7		$	27.3		$	68.2		$	(7.0	)	488.2
	Selling, general and administrative expense																189.2
	Income taxes (including $18.3 related to affiliates' earnings)																94
	Net income																$	205
	Selected Balance Sheet Data
	Investments in affiliated companies	$	17.2		$	1.8		$	—		$	338.7		$	—		$	357.7
	Identifiable assets	$	4,358.30		$	1,229.40		$	286.7		$	813.3		$	249.8		$	6,937.50
	Capital Expenditures
	Portfolio investments and capital additions	$	810.6		$	163.6		$	18.4		$	32.3		$	5.6		$	1,030.50
														Other			GATX Consolidated
		Rail North America			Rail International			ASC			Portfolio Management
	2013 Profitability
	Revenues
	Lease revenue	$	758.9		$	180.2		$	4.2		$	31.9		$	—		$	975.2
	Marine operating revenue	—			—			223.5			51.6			—			275.1
	Other revenue	58.2			8.8			—			3.7			—			70.7
	Total Revenues	817.1			189			227.7			87.2			—			1,321.00
	Expenses
	Maintenance expense	228.2			42.9			22.9			—			—			294
	Marine operating expense	—			—			151.3			38.5			—			189.8
	Depreciation expense	176.7			43.2			12.1			23			—			255
	Operating lease expense	124.4			—			5.2			—			(0.2		)	129.4
	Other operating expense	18.4			5.3			—			2.4			—			26.1
	Total Expenses	547.7			91.4			191.5			63.9			(0.2		)	894.3
	Other Income (Expense)
	Net gain (loss) on asset dispositions	67.7			3.7			(1.3		)	15.5			—			85.6
	Interest expense, net	(106.0		)	(23.9		)	(6.2		)	(26.7		)	(3.8		)	(166.6		)
	Other (expense) income	(9.8		)	(1.1		)	0.2			1.4			0.9			(8.4		)
	Share of affiliates' earnings (pretax)	10.3			21.1			—			60.9			—			92.3
	Segment profit (loss)	$	231.6		$	97.4		$	28.9		$	74.4		$	(2.7	)	429.6
	Selling, general and administrative expense																178.3
	Income taxes (including $16.5 related to affiliates' earnings)																82
	Net income																$	169.3
	Selected Balance Sheet Data
	Investments in affiliated companies	$	31.4		$	2		$	—		$	320.9		$	—		$	354.3
	Identifiable assets	$	3,710.50		$	1,297.10		$	271		$	856.9		$	414.1		$	6,549.60
	Capital Expenditures
	Portfolio investments and capital additions	$	502.4		$	168.5		$	11.2		$	170.5		$	7		$	859.6
														Other			GATX Consolidated
		Rail North America			Rail International			ASC			Portfolio Management
	2012 Profitability
	Revenues
	Lease revenue	$	713.9		$	161.2		$	4.3		$	37.6		$	—		$	917
	Marine operating revenue	—			—			239.1			26.4			—			265.5
Other revenue	51.4			6.5			—			2.8			—			60.7
Total Revenues	765.3			167.7			243.4			66.8			—			1,243.20
Expenses
Maintenance expense	201.4			46.6			21.7			—			—			269.7
Marine operating expense	—			—			160.3			22.1			—			182.4
Depreciation expense	167.7			36.1			11.9			21.7			—			237.4
Operating lease expense	126.5			—			3.8			0.2			(0.3		)	130.2
Other operating expense	18.5			5.1			(0.3		)	0.9			0			24.2
Total Expenses	514.1			87.8			197.4			44.9			(0.3		)	843.9
Other Income (Expense)
Net gain on asset dispositions	58.6			1.7			—			19.2			—			79.5
Interest expense, net	(101.9		)	(24.5		)	(7.1		)	(27.7		)	(5.4		)	(166.6		)
Other (expense) income	(5.1		)	(6.1		)	(1.4		)	3.4			1			(8.2		)
Share of affiliates' earnings (pretax)	6.5			(18.3		)	—			33.4			—			21.6
Segment profit (loss)	$	209.3		$	32.7		$	37.5		$	50.2		$	(4.1	)	325.6
Selling, general and administrative expense																160.2
Income taxes (including $2.0 related to affiliates' earnings)																28.1
Net income																$	137.3
Selected Balance Sheet Data
Investments in affiliated companies	$	46.9		$	77.2		$	—		$	377.9		$	—		$	502
Identifiable assets	$	3,601.10		$	1,105.80		$	284.2		$	797.4		$	266.9		$	6,055.40
Capital Expenditures
Portfolio investments and capital additions	$	465.9		$	200.1		$	12.6		$	83.5		$	7.9		$	770

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (unaudited)
		First		Second Quarter		Third Quarter		Fourth Quarter		Total
		Quarter
		In millions, except per share data
	2014
	Total revenues	$	286.6	$	365.8	$	397.2	$	401.4	$	1,451.00
	Net income	$	42.1	$	53.1	$	51.3	$	58.5	$	205
	Per Share Data (1)
	Basic	$	0.92	$	1.17	$	1.16	$	1.32	$	4.55
	Diluted	$	0.9	$	1.15	$	1.14	$	1.3	$	4.48
	2013
	Total revenues	$	272.3	$	338.9	$	353.2	$	356.6	$	1,321.00
	Net income	$	27.1	$	35.1	$	53.8	$	53.3	$	169.3
	Per Share Data (1)
	Basic	$	0.58	$	0.75	$	1.16	$	1.16	$	3.64
	Diluted	$	0.57	$	0.74	$	1.15	$	1.14	$	3.59
	___________________
	-1	Quarterly earnings per share may not be additive, as per share amounts are computed independently for each quarter and the full year is based on the respective weighted average common shares and common stock equivalents outstanding.

Description_of_Business_Detail

Description of Business (Details)	12 Months Ended
	Dec. 31, 2014
	Segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments	4

Accounting_Changes_Accounting_

Accounting Changes Accounting Changes (Details) (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Depreciation, Nonproduction	$273.50	$255	$237.40
Service Life [Member]
Property, Plant and Equipment [Line Items]
Depreciation, Nonproduction	21.9
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	$14
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Diluted Earnings Per Share	$0.31
Railcars [Member]
Property, Plant and Equipment [Line Items]
Average Increase (Decrease) in Estimated Railcar Useful Life	2 years 2 months 12 days
Railcars [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	27 years	30 years
Railcars [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	42 years	38 years

Significant_Accounting_Policie3

Significant Accounting Policies (Details 1)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Minimum [Member] | Railcars [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	27 years	30 years
Minimum [Member] | Locomotives [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	10 years
Minimum [Member] | Buildings [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	40 years
Minimum [Member] | Leasehold Improvements [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	5 years
Minimum [Member] | Marine vessels [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	30 years
Minimum [Member] | Industrial Equipment [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	5 years
Maximum [Member] | Railcars [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	42 years	38 years
Maximum [Member] | Locomotives [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	20 years
Maximum [Member] | Buildings [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	50 years
Maximum [Member] | Leasehold Improvements [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	15 years
Maximum [Member] | Marine vessels [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	65 years
Maximum [Member] | Industrial Equipment [Member]
Estimated lives of useful depreciable assets
Estimated useful lives of depreciable assets, minimum	30 years

Significant_Accounting_Policie4

Significant Accounting Policies (Gain on Asset Dispositions) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Significant Acquisitions and Disposals [Line Items]
Disposition gains	$63.10	$60	$42.70
Residual sharing income	9.4	10.8	22.6
Non-remarketing disposition gains	16	20.7	19.2
Asset impairments	-1.3	-5.9	-5
Net Gain on Asset Dispositions	$87.20	$85.60	$79.50

Significant_Accounting_Policie5

Significant Accounting Policies (Details Textual) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	Entity
Accounting Policies [Abstract]
Wholly-owned bankruptcy remote special-purpose corporations	2
Interest expense net of interest income on bank deposits	$0.90	$1.20	$1.90

Significant_Accounting_Policie6

Significant Accounting Policies Foreign Currency (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Foreign Currency [Abstract]
Foreign Currency Transaction Gain (Loss), before Tax	($3.40)	$2.10	$0.50

Supplemental_Cash_Flow_and_Non2

Supplemental Cash Flow and Noncash Investing Transactions (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
	Car		Vessel
			Car
Noncash or Part Noncash Divestitures [Line Items]
Number of railcars received	62		640
Number of vessels received			5
Noncash or Part Noncash Acquisition, Value of Assets Acquired	$1.10		$174.70
Fair Value of Assets Acquired	1.1		22.9	0
Supplemental Cash Flow Information
Interest paid	142.6	[1]	148.7	162.3
Income taxes paid (refunded), net	18.7		7.4	11.1
Portfolio proceeds	$264		$385.30	$288.90
[1]	(1) Interest paid consisted of interest on debt obligations, interest rate swaps (net of interest received), and capital leases. The interest expense we capitalized as part of the cost of construction of major assets was immaterial for all periods presented.

Supplemental_Cash_Flow_and_Non3

Supplemental Cash Flow and Noncash Investing Transactions (Details Textual)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2013
	USD ($)	USD ($)	USD ($)	Singco/Somagas [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]
	Car	Car		USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	EUR (€)	USD ($)	EUR (€)
Noncash or Part Noncash Divestitures [Line Items]
Portfolio proceeds	$264	$385.30	$288.90		$0	$91.10	$0	$77	€ 68.20	$91.10	€ 67.50
Supplemental Cash Flow and Noncash Investing and Financing Transactions (Textual) [Abstract]
Aggregate fair value of liquidating distributions	$1.10	$22.90	$0	$151.80
Number of railcars received	62	640

Leases_Details

Leases (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Direct Financing [Abstract]
Total minimum lease payments receivable, Direct Financing	$204.80	$270.20
Estimated non-guaranteed residual value of leased assets, Direct Financing	68.5	79.8
Unearned income, Direct Financing	-98.6	-142.7
Finance leases, Direct Financing	$174.70	$207.30

Leases_Details_1

Leases (Details 1) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Minimum Future Receipts
2013, Finance Leases	$26.30
2014, Finance Leases	25.2
2015, Finance Leases	23.9
2016, Finance Leases	22.2
2017, Finance Leases	11.8
Years thereafter, Finance Leases	95.4
Total, Finance Leases	204.8
2013, Operating Leases	923.4	[1]
2014, Operating Leases	740.3	[1]
2015, Operating Leases	584.1	[1]
2016, Operating Leases	464.7	[1]
2017, Operating Leases	370	[1]
Years thereafter, Operating Leases	770.4	[1]
Total future receipts from leases	3,852.90	[1]
2013, Total	949.7
2014, Total	765.5
2015, Total	608
2016, Total	486.9
2017, Total	381.8
Years thereafter, Total	865.8
Total	$4,057.70
[1]	(1) The future contractual receipts due under our full-service operating leases include executory costs such as maintenance, car taxes, and insurance.

Leases_Details_2

Leases (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Assets that are financed with capital lease obligations
Less: allowance for depreciation	($75.30)	($71.40)
Capital leased assets, net	7.8	10
Marine vessels [Member]
Assets that are financed with capital lease obligations
Capital leased assets, gross	$83.10	$81.40

Leases_Details_3

Leases (Details 3) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Capital Leases
2013, Capital Leases	$3.10
2014, Capital Leases	2.7
2015, Capital Leases	1.1
2016, Capital Leases	0
2017, Capital Leases	0
Years thereafter, Capital Leases	0
Capital Leases, Future Minimum Payments Due, Total	6.9
Less: amounts representing interest	-0.6
Present value of future minimum capital lease payments	6.3		8.9
Recourse Operating Leases [Member]
Operating Leases
2013, Operating Lease	86.3
2014, Operating Lease	89
2015, Operating Lease	94.2
2016, Operating Lease	85.6
2017, Operating Lease	81.5
Years thereafter, Operating Leases	310.1
Total, Operating Leases	746.7
Nonrecourse Operating Leases [Member]
Operating Leases
2013, Operating Lease	11	[1]
2014, Operating Lease	8.1	[1]
2015, Operating Lease	9.5	[1]
2016, Operating Lease	9	[1]
2017, Operating Lease	9.7	[1]
Years thereafter, Operating Leases	18.7	[1]
Total, Operating Leases	$66	[1]
[1]	(1) The amounts shown are primarily the rental payments of one wholly owned, bankruptcy-remote special purpose corporations. We consolidate these rentals for accounting purposes, but they are not our legal obligations.

Leases_Details_Textual

Leases (Details Textual) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014							Dec. 31, 2013	Dec. 31, 2012
	Corporations
Operating Leased Assets [Line Items]
Schedule of Capital Leased Assets [Table Text Block]	The following table shows assets we financed with capital lease obligations as of December 31 (in millions):
		2014			2013
	Marine vessels	$	83.1		$	81.4
	Less: allowance for depreciation	(75.3		)	(71.4		)
		$	7.8		$	10
Operating Leases, Rent Expense	$112.90							$134	$133.30
Leases (Textual) [Abstract]
Income from leveraged leases, net of taxes									0.2
Rental income from usage rents	83.9							21.3	18.2
Property, Plant and Equipment, Schedule of Significant Acquisitions and Disposals [Table Text Block]	18500
Deferred initial direct costs of direct financial leases	$0.30							$0.40
Number of corporations	1
Railroad Transportation Equipment [Member]
Operating Leased Assets [Line Items]
Schedule of Capital Leased Assets [Table Text Block]	23000
Marine vessels [Member]
Operating Leased Assets [Line Items]
Schedule of Capital Leased Assets [Table Text Block]	1

Investments_in_Affiliated_Comp2

Investments in Affiliated Companies (Significant Investments in Affiliates) (Details 1)

12 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

USD ($)

USD ($)

USD ($)

Rolls Royce Partners Finance [Member]

Cardinal Marine Investments Llc [Member]

Adler Funding Llc [Member]

Other Affiliates [Member]

RRPF Joint Ventures [Member]

Singco/Somagas [Member]

Intermodal Investment Fund V and VII [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

Vessel

USD ($)

USD ($)

USD ($)

USD ($)

Joint_Venture

USD ($)

USD ($)

USD ($)

EUR (€)

USD ($)

EUR (€)

Investments in and Advances to Affiliates [Line Items]

Advances to Affiliate

$16.30

$24.20

Equity Method Investment, Net Sales Proceeds

19.4

55.6

12.5

18.3

Portfolio proceeds and other

264

385.3

288.9

77

68.2

91.1

67.5

Number of vessels received

5

Investments in and Advances to Affiliates, Schedule of Investments [Abstract]

Investments in affiliated companies

357.7

354.3

502

293.6

[1]

45.1

16.9

2.1

GATX's Percentage Ownership

50.00%

[1]

50.00%

12.50%

37.50%

37.50%

Number of joint venture investments

14

Fair Value of Assets Acquired

$1.10

$22.90

$0

$151.80

[1]

(1) Combined investment balances of fourteen separate joint ventures (collectively, the "RRPF affiliates")

Loans_Details

Loans (Details)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2013
	USD ($)	USD ($)	USD ($)	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]	Aae Cargo Ag [Member]
				USD ($)	EUR (€)	USD ($)	EUR (€)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Portfolio proceeds and other	$264	$385.30	$288.90	$77	€ 68.20	$91.10	€ 67.50
Portfolio Proceeds, Principal				76.2	67.5
Portfolio Proceeds, Interest				0.8	0.7
2014	86.4
2015	4.3
2016	2
2017	4.6
2018	0
Thereafter	0
Loans receivables, outstanding	$97.30	$122.70

Investments_in_Affiliated_Comp3

Investments in Affiliated Companies (Share of Affiliate Earnings) (Details 2) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pre tax share of affiliates earnings by segment
Share of affiliates' earnings (pre-tax)	$67.80	$92.30	$21.60
Provision for Income Taxes, Equity Method Investment	-18.3	-16.5	-2
Share of Affiliates' Earnings	49.5	75.8	19.6
Rail North America [Member]
Pre tax share of affiliates earnings by segment
Share of affiliates' earnings (pre-tax)	7.9	10.3	6.5
Rail International [Member]
Pre tax share of affiliates earnings by segment
Share of affiliates' earnings (pre-tax)	-0.3	21.1	-18.3
Portfolio Management [Member]
Pre tax share of affiliates earnings by segment
Share of affiliates' earnings (pre-tax)	$60.20	$60.90	$33.40

Investments_in_Affiliated_Comp4

Investments in Affiliated Companies (Investments and Distributions) (Details 3) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
		Vessel
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Net Sales Proceeds	$19.40	$55.60	$12.50
Number of vessels received		5
Payments to Acquire Equity Method Investments	15.3	101.3	29.7
Proceeds from Equity Method Investment, Dividends or Distributions	54.2	47	53.2
Rail North America [Member]
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Equity Method Investments	0	0	0
Proceeds from Equity Method Investment, Dividends or Distributions	20	0	14.9
Rail International [Member]
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Equity Method Investments	0	0	0
Proceeds from Equity Method Investment, Dividends or Distributions	0	0	0
Portfolio Management [Member]
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Equity Method Investments	15.3	101.3	29.7
Proceeds from Equity Method Investment, Dividends or Distributions	34.2	47	38.3
Enerven Compression Llc [Member]
Schedule of Equity Method Investments [Line Items]
Reversal of Impairment Loss		$1.10

Investments_in_Affiliated_Comp5

Investments in Affiliated Companies (Operating Results, Affiliates) (Details 4) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity Method Investments and Joint Ventures [Abstract]
Gain on Sale of Investments		$2.50
Operating results for all affiliated companies of GATX
Revenues	339	334.5	651.8
Gains on sales of assets	33.7	43.5	57.4
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$99.60	$108.60	$75.30

Investments_in_Affiliated_Comp6

Investments in Affiliated Companies (Balance Sheet, Affiliates) (Details 5) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Summarized balance sheet for all affiliated companies
Current assets	$211.60	$200.50
Noncurrent assets	3,195.10	2,989.20
Total assets	3,406.70	3,189.70
Current liabilities	378.4	159.6
Noncurrent liabilities	2,388.20	2,408.80
Shareholders’ equity	640.1	621.3
Total liabilities and shareholders' equity	$3,406.70	$3,189.70

Investments_in_Affiliated_Comp7

Investments in Affiliated Companies (Summarized Financial Data-RRPF) (Details 6) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Income Statement [Abstract]
Lease revenue	$339		$334.50		$651.80
Income taxes			-15.2		-9.2
Net income	99.6		108.6		75.3
Assets [Abstract]
Current assets	211.6		200.5
Other noncurrent assets	3,195.10		2,989.20
Total assets	3,406.70		3,189.70
Liabilities and Equity [Abstract]
Current liabilities	378.4		159.6
Long-term debt	2,388.20		2,408.80
Shareholders’ equity	640.1		621.3
Total liabilities and shareholders' equity	3,406.70		3,189.70
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
number of aircraft engines	433
Income Statement [Abstract]
Depreciation expense	-140.7		-120.2		-115.1
Interest expense	-59.5		-65.8		-64.8
Other expenses	-11.8		-10.2		-16.3
Gains on sales of assets	22.7		35.2		35.9
Income before income taxes	112.3		106.3		93
Income taxes	-17.3	[1]	0.4	[1]	-3.8	[1]
Net income	95		106.7		89.2
Assets [Abstract]
Current assets	146.3		151
Operating assets, net of accumulated depreciation of $744.5 and $651.8	2,988.10	[2]	2,619.60	[2]
Total assets	3,134.40		2,770.60
Liabilities and Equity [Abstract]
Current liabilities	358.5		141
Long-term debt	2,012.90		1,963.10
Other liabilities	218.1		212.4
Shareholders’ equity	544.9		454.1
Total liabilities and shareholders' equity	3,134.40		2,770.60
RRPF Joint Ventures [Member] | Third Parties [Member]
Income Statement [Abstract]
Lease revenue	176.9		147.6		140.4
RRPF Joint Ventures [Member] | Rolls-Royce [Member]
Income Statement [Abstract]
Lease revenue	$124.70		$119.70		$112.90
[1]	(1) Represents income taxes directly attributable to the RRPF affiliates in the United Kingdom. Several of the RRPF affiliates are flow through entities and income taxes are incurred at the shareholder level. Amounts shown for 2013 and 2012 include tax benefits of approximately $15.2 million and $9.2 million, attributable to statutory rate decreases in the United Kingdom.
[2]	(a) All operating assets were pledged as collateral for long-term debt obligations.

Investments_in_Affiliated_Comp8

Investments in Affiliated Companies (Future Lease Receipts) (Details 7) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Schedule of Equity Method Investments [Line Items]
2013	$923.40	[1]
2014	740.3	[1]
2015	584.1	[1]
2016	464.7	[1]
2017	370	[1]
Years thereafter	770.4	[1]
Total future receipts from leases	3,852.90	[1]
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
2013	303.5
2014	271.1
2015	239.7
2016	218.1
2017	167.8
Years thereafter	428.5
Total future receipts from leases	1,628.70
RRPF Joint Ventures [Member] | Rolls-Royce [Member]
Schedule of Equity Method Investments [Line Items]
2013	144.6
2014	129.3
2015	109.7
2016	102.4
2017	97.1
Years thereafter	212.3
Total future receipts from leases	795.4
RRPF Joint Ventures [Member] | Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
2013	158.9
2014	141.8
2015	130
2016	115.7
2017	70.7
Years thereafter	216.2
Total future receipts from leases	$833.30
[1]	(1) The future contractual receipts due under our full-service operating leases include executory costs such as maintenance, car taxes, and insurance.

Investments_in_Affiliated_Comp9

Investments in Affiliated Companies (Future Debt Maturities) (Details 8) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Schedule of Equity Method Investments [Line Items]
2015	$529.20
2016	639.2
2017	455.4
2018	507.5
2019	592.3
Thereafter	1,480.20
Total debt principal	4,203.80		3,842
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
2015	277
2016	323.3
2017	252.2
2018	106.9
2019	426
Thereafter	904.5
Total debt principal	$2,289.90	[1]
[1]	(1) All debt obligations are nonrecourse to the shareholders

Recovered_Sheet1

Investments in Affiliated Companies (Textual) (Details)

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

USD ($)

USD ($)

USD ($)

RRPF Joint Ventures [Member]

RRPF Joint Ventures [Member]

RRPF Joint Ventures [Member]

RRPF Joint Ventures [Member]

RRPF Joint Ventures [Member]

RRPF Joint Ventures [Member]

Fair Value, Measurements, Nonrecurring [Member]

Fair Value, Measurements, Nonrecurring [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

Singco/Somagas [Member]

Singco/Somagas [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

Aae Cargo Ag [Member]

USD ($)

USD ($)

USD ($)

Minimum [Member]

Maximum [Member]

Aircraft Engines [Member]

Fair Value, Inputs, Level 3 [Member]

Accumulated Other-than-Temporary Impairment [Member]

USD ($)

EUR (€)

USD ($)

EUR (€)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

Business_Activity

USD ($)

Fair Value, Inputs, Level 3 [Member]

Joint_Venture

Equity Method Investments [Member]

USD ($)

Schedule of Equity Method Investments [Line Items]

Noncash or Part Noncash Acquisition, Value of Assets Acquired

$1.10

$174.70

$101.30

Loans to affiliated companies

16.3

24.2

Asset Impairment Charges

1.3

5.9

5

14.8

14.8

GATX ownership percentage in joint venture

50.00%

Number of joint venture investments

14

Number of business activities

2

Estimated useful lives of depreciable assets

25 years

Lease term

7 years

10 years

Share of affiliates' earnings (net of tax)

49.5

75.8

19.6

42.2

46.5

36.7

Noncontrolling Interest, Ownership Percentage by Parent

37.50%

37.50%

Gain on Sale of Investments

2.5

9.3

gmt_SalePrice

114.1

Proceeds from Divestiture of Businesses and Interests in Affiliates

23

Portfolio proceeds

$264

$385.30

$288.90

$77

€ 68.20

$91.10

€ 67.50

$0

$91.10

$0

Recovered_Sheet2

Investments in Affiliated Companies Advances to Affiliates (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Investments in and Advances to Affiliates, Schedule of Investments [Abstract]
Advances to Affiliate	$16.30	$24.20

Variable_Interest_Entities_Det

Variable Interest Entities (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Type of Entity	one
Variable Interest, Held by Entity [Member]
Carrying amounts of assets and liabilities of the VIE
Operating assets, net of accumulated depreciation	88.1	[1]	$93	[1]
Nonrecourse debt	15.9		$25.40
[1]	(1) All operating assets are pledged as collateral on the nonrecourse debt.

Variable_Interest_Entities_Det1

Variable Interest Entities (Details 1) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Carrying amounts and maximum exposure to loss with respect to VIEs
Net Carrying Amount	$144.30	$126.10
Maximum Exposure to Loss	144.3	126.1
Investments in Affiliates [Member]
Carrying amounts and maximum exposure to loss with respect to VIEs
Net Carrying Amount	143.9	125.5
Maximum Exposure to Loss	143.9	125.5
Other investment [Member]
Carrying amounts and maximum exposure to loss with respect to VIEs
Net Carrying Amount	0.4	0.6
Maximum Exposure to Loss	$0.40	$0.60

Debt_Details

Debt (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Commercial Paper and Borrowings Under Bank Credit Facilities
Balance	$72.10	$23.60
Weighted average interest rate	0.56%	0.80%
Outstanding balances of debt obligations and the applicable interest rates
Total debt principal	4,203.80	3,842
Debt discount, net	-8.6	-8.9
Debt adjustment for fair value hedges	0.6	5.4
Total Debt	4,195.80	3,838.50
Recourse Fixed Rate Debt Unsecured One [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	14-Apr-05
Final Maturity	15-Apr-15
Fixed Interest Rate	5.70%
Total Debt	100	100
Recourse Fixed Rate Debt Unsecured Two [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	5-Feb-10
Final Maturity	15-May-15
Fixed Interest Rate	4.75%
Total Debt	250	250
Recourse Fixed Rate Debt Unsecured Three [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	22-Dec-05
Final Maturity	22-Dec-15
Fixed Interest Rate	5.75%
Total Debt	70	85
Recourse Fixed Rate Debt Unsecured Four [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	3-Mar-06
Final Maturity	1-Mar-16
Fixed Interest Rate	5.80%
Total Debt	250	200
Recourse Fixed Rate Debt Unsecured Five [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	19-Nov-10
Final Maturity	15-Jul-16
Fixed Interest Rate	3.50%
Total Debt	200	250
Recourse Fixed Rate Debt Unsecured Six [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	20-Sep-11
Final Maturity	15-Jul-16
Fixed Interest Rate	3.50%
Total Debt	100	100
Recourse Fixed Rate Debt Unsecured Seven [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	4-Mar-14
Final Maturity	4-Mar-17
Fixed Interest Rate	1.25%
Total Debt	300	0
Recourse Fixed Rate Debt Unsecured Eight [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	6-Feb-08
Final Maturity	15-Feb-18
Fixed Interest Rate	6.00%
Total Debt	200	200
Recourse Fixed Rate Debt Unsecured Nine [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	19-Mar-13
Final Maturity	30-Jul-18
Fixed Interest Rate	2.38%
Total Debt	250	250
Recourse Fixed Rate Debt Unsecured Ten [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	27-Dec-10
Final Maturity	31-Oct-18
Fixed Interest Rate	3.84%
Total Debt	15.7	22
Recourse Fixed Rate Debt Unsecured Eleven [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	29-Nov-10
Final Maturity	30-Nov-18
Fixed Interest Rate	3.70%
Total Debt	12.1	17.2
Recourse Fixed Rate Debt Unsecured Twelve [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	19-Nov-13
Final Maturity	15-Mar-19
Fixed Interest Rate	2.50%
Total Debt	300	300
Recourse Fixed Rate Debt Unsecured Thirteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	4-Mar-14
Final Maturity	30-Jul-19
Fixed Interest Rate	2.50%
Total Debt	250	0
Recourse Fixed Rate Debt Unsecured Fourteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	31-Oct-14
Final Maturity	30-Mar-20
Fixed Interest Rate	2.60%
Total Debt	250	0
Recourse Fixed Rate Debt Unsecured Fifteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	27-May-11
Final Maturity	1-Jun-21
Fixed Interest Rate	4.85%
Total Debt	250	250
Recourse Fixed Rate Debt Unsecured Sixteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	20-Sep-11
Final Maturity	1-Jun-21
Fixed Interest Rate	4.85%
Total Debt	50	50
Recourse Fixed Rate Debt Unsecured Seventeen [Member] [Domain]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	11-Jun-12
Final Maturity	15-Jun-22
Fixed Interest Rate	4.75%
Total Debt	250	250
Recourse Fixed Rate Debt Unsecured Eighteen [Member] [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	19-Mar-13
Final Maturity	30-Mar-23
Fixed Interest Rate	3.90%
Total Debt	250	250
Recourse Fixed Rate Debt Unsecured Nineteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	4-Mar-14
Final Maturity	15-Mar-44
Fixed Interest Rate	5.20%
Total Debt	300	0
Recourse Fixed Rate Debt Unsecured Twenty [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	30-Apr-09
Final Maturity	15-May-14
Fixed Interest Rate	8.75%
Total Debt	0	300
Recourse Fixed Rate Debt [Member]
Outstanding balances of debt obligations and the applicable interest rates
Total Debt	3,647.80	2,874.20
Recourse Floating Rate Debt Unsecured One [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	15-Dec-10
Final Maturity	31-Oct-15
Floating Interest Rate	1.47%
Total Debt	24.8	36.4
Recourse Floating Rate Debt Unsecured Three [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	2-Sep-11
Final Maturity	31-Aug-16
Floating Interest Rate	1.13%
Total Debt	8	11.5
Recourse Floating Rate Debt Unsecured Four [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	29-Mar-06
Final Maturity	30-Sep-16
Floating Interest Rate	2.08%
Total Debt	18.9	32.2
Recourse Floating Rate Debt Secured One [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	19-Dec-11
Final Maturity	19-Dec-20
Floating Interest Rate	2.10%
Total debt principal	0	91.1
Recourse Floating Rate Debt Unsecured Five [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	29-Jun-07
Final Maturity	30-Sep-16
Floating Interest Rate	2.03%
Total Debt	8.5	14.4
Recourse Floating Rate Debt Unsecured Six [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	18-Dec-07
Final Maturity	31-Oct-16
Floating Interest Rate	1.98%
Total Debt	12.7	21.6
Recourse Floating Rate Debt Unsecured Seven [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	21-Dec-12
Final Maturity	21-Dec-17
Floating Interest Rate	1.39%
Total Debt	100	100
Recourse Floating Rate Debt Unsecured Eight [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	22-Jan-13
Final Maturity	21-Dec-17
Floating Interest Rate	1.39%
Total Debt	10	70
Recourse Floating Rate Debt Secured Two [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	6-Dec-11
Final Maturity	31-Aug-16
Floating Interest Rate	1.57%
Total Debt	15.3	22.1
Recourse Floating Rate Debt Unsecured Nine [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	31-Aug-12
Final Maturity	31-Dec-19
Floating Interest Rate	2.33%
Total Debt	60.5	68.7
Recourse Floating Rate Debt Unsecured Ten [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	27-Jun-13
Final Maturity	31-Dec-20
Floating Interest Rate	1.87%
Total debt principal	121	137.5
Recourse Floating Rate Debt Un Secured Eleven [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	30-Oct-13
Final Maturity	31-Dec-20
Floating Interest Rate	1.91%
Total debt principal	30.2	34.4
Recourse Floating Rate Debt Un Secured Twelve [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	5-May-14
Final Maturity	31-Dec-20
Floating Interest Rate	1.99%
Total debt principal	30.2	0
Recourse Floating Rate Debt Un Secured Thirteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	28-Aug-14
Final Maturity	28-Aug-24
Floating Interest Rate	1.54%
Total debt principal	100	0
Recourse Floating Rate Debt Unsecured Fourteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	1-Mar-10
Final Maturity	28-Feb-15
Floating Interest Rate	1.83%
Total debt principal	0	13.7
Recourse Floating Rate Debt Unsecured Fifteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	12-Dec-11
Final Maturity	12-Jun-17
Floating Interest Rate	1.63%
Total debt principal	0	103.5
Recourse Floating Rate Debt Unsecured Sixteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	12-Aug-13
Final Maturity	12-Jun-17
Floating Interest Rate	1.63%
Total debt principal	0	71.1
Recourse Floating Rate Debt Unsecured Seventeen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	12-Jan-12
Final Maturity	12-Jun-17
Floating Interest Rate	1.63%
Total debt principal	0	31.5
Recourse Floating Rate Debt Unsecured Eighteen [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	21-Feb-13
Final Maturity	21-Dec-17
Floating Interest Rate	1.81%
Total debt principal	0	35
Total Recourse Floating Rate Debt [Member]
Outstanding balances of debt obligations and the applicable interest rates
Total debt principal	540.1	894.7
Nonrecourse Fixed Rate Debt Secured One [Member]
Outstanding balances of debt obligations and the applicable interest rates
Date of Issue	30-Sep-97
Final Maturity	20-Sep-16
Floating Interest Rate	6.69%
Total debt principal	15.9	25.4
Total Nonrecourse Fixed Rate Debt [Member]
Outstanding balances of debt obligations and the applicable interest rates
Total debt principal	15.9	25.4
Nonrecourse Floating Rate Debt Secured One [Member]
Outstanding balances of debt obligations and the applicable interest rates
Final Maturity	8-May-14
Floating Interest Rate	1.40%
Total debt principal	$0	$47.70

Debt_Details_1

Debt (Details 1) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Maturities of GATX's debt obligations
2015	$529.20
2016	639.2
2017	455.4
2018	507.5
2019	592.3
Thereafter	1,480.20
Total debt principal	$4,203.80	$3,842

Debt_Details_Textual

Debt (Details Textual) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Line of Credit Facility [Line Items]
Non-Recourse Debt	$15.90	$72.60
Operating assets pledged as collateral for notes	95.9
Other Short-term Borrowings	72.1	23.6
Fixed charge coverage ratio	2.5
Minimum debt covenant fixed charge coverage ratio	1.2
Amount of secured debt available to be borrowed in accordance with public debt covenants	1,283.10
Line of Credit US [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	575
Availability under credit facility	506
Annual commitment fees	0.8	1	1.2
Line of Credit Europe [Member]
Line of Credit Facility [Line Items]
Maximum amount of GRE transfer to GATX relating to loans and dividends	111.3
Restricted net assets	391.2
Fair Value Hedging [Member]
Line of Credit Facility [Line Items]
Derivative, Number of Instruments Held	8	3
Commercial Paper [Member]
Line of Credit Facility [Line Items]
Other Short-term Borrowings	$69

Fair_Value_Disclosure_Details

Fair Value Disclosure (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Assets
Available for sale equity securities	$4.40		$4.70
Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Assets
Interest rate derivatives	1.8	[1]	6	[1]
Liabilities
Interest rate derivatives	5.9	[1]	0.8	[1]
Fair Value, Measurements, Recurring [Member] | Not Designated as Hedging Instrument [Member]
Assets
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value	9.7	[2]
Liabilities
Interest rate derivatives			0.2	[2]
Foreign exchange rate derivatives	-1.6	[2]	-2.6	[2]
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale equity securities	4.4		4.7
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Assets
Interest rate derivatives	0	[1]	0	[1]
Liabilities
Interest rate derivatives	0	[1]	0	[1]
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Not Designated as Hedging Instrument [Member]
Assets
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value	0	[2]
Liabilities
Interest rate derivatives			0	[2]
Foreign exchange rate derivatives	0	[2]	0	[2]
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale equity securities	0		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Assets
Interest rate derivatives	1.8	[1]	6	[1]
Liabilities
Interest rate derivatives	5.9	[1]	0.8	[1]
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Not Designated as Hedging Instrument [Member]
Assets
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value	9.7	[2]
Liabilities
Interest rate derivatives			0.2	[2]
Foreign exchange rate derivatives	-1.6	[2]	-2.6	[2]
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Available for sale equity securities	0		0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]
Assets
Interest rate derivatives	0	[1]	0	[1]
Liabilities
Interest rate derivatives	0	[1]	0	[1]
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Not Designated as Hedging Instrument [Member]
Assets
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value	0	[2]
Liabilities
Interest rate derivatives			0	[2]
Foreign exchange rate derivatives	0	[2]	0	[2]
Other Expense [Member] | Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	-11.4		-0.6		5
Other Expense [Member] | Aae Cargo Ag [Member] | Not Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$10.40
[1]	(1) Designated as hedges
[2]	(2) Not designated as hedges

Fair_Value_Disclosure_Details_

Fair Value Disclosure (Details 1) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	$1.30	$5.90	$5
Investments in Affiliates, Subsidiaries, Associates, and Joint Ventures, Fair Value Disclosure			32.9
Operating assets and facilities, net	5,688	5,070.30
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges			14.8
Equipment [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset Impairment Charge [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset Impairment Charges	0.7	2.5	0.7
Equipment [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating assets and facilities, net	$2.50	$9.60	$0.70

Fair_Value_Disclosure_Details_1

Fair Value Disclosure (Details 2) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Interest Expense [Member] | Fair Value Hedging [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Interest expense	$4.70	[1]	$4.90	[1]	$5	[1]
Interest Expense [Member] | Cash Flow Hedges [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Effective portion reclassified from accumulated other comprehensive loss	4.9		5.1		4.2
Other Comprehensive Income (Loss) [Member] | Cash Flow Hedges [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Other comprehensive loss (effective portion)	5.1		-0.7		0.2
Operating Expense [Member] | Cash Flow Hedges [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Effective portion reclassified from accumulated other comprehensive loss	3.2		1.5		1.4
Other Nonoperating Income (Expense) [Member] | Cash Flow Hedges [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Effective portion reclassified from accumulated other comprehensive loss	-2.1		0		0
Other Expense [Member] | Non-designated [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Other expense	-11.4		-0.6		5
Other Expense [Member] | Cash Flow Hedges [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Other expense	$0		$0		($0.10)
[1]	(1) The fair value adjustments related to the underlying debt equally offset the amounts recognized in interest expense.

Fair_Value_Disclosure_Details_2

Fair Value Disclosure (Details 3) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Assets
Loans	$97.30	$122.70
Liabilities
Non-Recourse Debt	15.9	72.6
Carrying Amount [Member]
Assets
Investment Funds	1.5	1.7
Loans		122.7
Liabilities
Recourse fixed rate debt	3,639.90	2,871.20
Recourse floating rate debt	540	894.7
Nonrecourse debt		72.6
Estimate of Fair Value Measurement [Member]
Assets
Investment Funds	2.4	4
Loans	97.4	121.5
Liabilities
Recourse fixed rate debt	3,775	2,994
Recourse floating rate debt	540	906.2
Nonrecourse debt	$16.60	$74.70

Fair_Value_Disclosure_Details_3

Fair Value Disclosure (Details Textual) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Disclosure (Textual) [Abstract]
Derivative, Notional Amount	$281.50	$0
Cash Flow Hedge Pre Tax Gain Loss to be Reclassified within Twelve Months	-6
Expected After tax reclassification of net losses from accumulated other comprehensive income to earnings in Next Twelve Months	3.8
Aggregate fair value of all derivative instruments with Net liability position	5.9
Derivative Asset, Notional Amount	$600	$200
Fair Value Hedging [Member]
Fair Value Disclosure (Textual) [Abstract]
Number of instruments, outstanding	8	3
Cash Flow Hedges [Member]
Fair Value Disclosure (Textual) [Abstract]
Number of instruments, outstanding	7	6

Pension_and_Other_PostRetireme2

Pension and Other Post-Retirement Benefits (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Change in Fair Value of Plan Assets
Company contributions	$1.80	$1.60	$1.60
Plan assets at end of year	457
Amount Recognized
Other liabilities	-86.6	-68.2
Accumulative other comprehensive loss:
After-tax amount recognized in accumulated other comprehensive loss	107.7	78.2	131.1	118.7
Defined Benefit Pension [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year	442.7	473.8
Service cost	5.9	6.7	5.7
Interest cost	20.7	18.4	19.7
Actuarial loss	67	-26.8
Benefits paid	31.2	30.3
Effect of foreign exchange rate changes	-2.4	0.9
Benefit obligation at end of year	502.7	442.7	473.8
Change in Fair Value of Plan Assets
Plan assets at beginning of year	447.8	409.1
Actual return on plan assets	40.3	65.9
Effect of exchange rate changes	-2.4	0.7
Company contributions	2.4	2.4
Benefits paid	31.2	30.3
Plan assets at end of year	456.9	447.8	409.1
Funded Status at end of year	-45.8	5.1
Amount Recognized
Other liabilities	-45.8	5.1
Accumulative other comprehensive loss:
Net actuarial loss	170.9	127.6
Prior service credit (cost)	-2.1	-3.1
Accumulated other comprehensive loss	168.8	124.5
After-tax amount recognized in accumulated other comprehensive loss	105.4	77.6
Retiree Health and Life [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year	40.4	48.1
Service cost	0.1	0.2	0.2
Interest cost	1.6	1.6	2
Actuarial loss	2.6	-6.2
Benefits paid	3.9	3.3
Effect of foreign exchange rate changes	0	0
Benefit obligation at end of year	40.8	40.4	48.1
Change in Fair Value of Plan Assets
Plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Effect of exchange rate changes	0	0
Company contributions	3.9	3.3
Benefits paid	3.9	3.3
Plan assets at end of year	0	0	0
Funded Status at end of year	-40.8	-40.4
Amount Recognized
Other liabilities	-40.8	-40.4
Accumulative other comprehensive loss:
Net actuarial loss	3.3	0.6
Prior service credit (cost)	0.4	0.4
Accumulated other comprehensive loss	3.7	1
After-tax amount recognized in accumulated other comprehensive loss	$2.30	$0.60

Pension_and_Other_PostRetireme3

Pension and Other Post-Retirement Benefits (Details 1) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligations	$502.70	$67.80
Fair value of plan assets	456.9	40
Pension plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligations	170.6	66.4
Fair value of plan assets	$140.50	$40

Pension_and_Other_PostRetireme4

Pension and Other Post-Retirement Benefits (Details 2) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Pension [Member]
Components of pension and other post retirement benefit costs
Service cost	$5.90	$6.70	$5.70
Interest cost	20.7	18.4	19.7
Expected return on plan assets	-28.4	-27.5	-29.6
Amortization of unrecognized prior service credit	-1	-1	-1
Unrecognized net actuarial loss (gain)	11.3	14.9	9.9
Net periodic (benefit) cost	8.5	11.5	4.7
Retiree Health and Life [Member]
Components of pension and other post retirement benefit costs
Service cost	0.1	0.2	0.2
Interest cost	1.6	1.6	2
Expected return on plan assets	0	0	0
Amortization of unrecognized prior service credit	-0.1	-0.1	-0.1
Unrecognized net actuarial loss (gain)	-0.1	0	-0.1
Net periodic (benefit) cost	$1.50	$1.70	$2

Pension_and_Other_PostRetireme5

Pension and Other Post-Retirement Benefits (Details 3)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Domestic defined benefit pension plans [Member] | Salaried Funded and Unfunded Plans [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, benefit obligation	4.05%	4.80%
Rate of compensation and pension-in-payment increases, benefit obligation	2.50%	3.00%
Discount rate, net periodic cost (benefit)	4.80%	3.95%
Expected return on plan assets, net periodic cost (benefit)	7.60%	7.75%
Rate of compensation and pension-in-payment increases, net periodic cost (benefit)	3.00%	3.00%
Domestic defined benefit pension plans [Member] | Hourly Funded Plans [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, benefit obligation	4.10%	4.90%
Discount rate, net periodic cost (benefit)	4.90%	4.05%
Expected return on plan assets, net periodic cost (benefit)	6.90%	6.80%
Foreign Funded Pension Plans, Defined Benefit [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, benefit obligation	3.20%	4.40%
Rate of compensation and pension-in-payment increases, benefit obligation	2.90%	3.40%
Discount rate, net periodic cost (benefit)	4.40%	4.25%
Expected return on plan assets, net periodic cost (benefit)	5.40%	5.34%
Rate of compensation and pension-in-payment increases, net periodic cost (benefit)	3.40%	3.00%
Retiree Health and Life [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, net periodic cost (benefit)	4.20%	3.65%
Retiree Health and Life [Member] | Salaried Health [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, benefit obligation	3.65%	4.20%
Retiree Health and Life [Member] | Hourly Health [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, benefit obligation	3.85%	4.60%
Discount rate, net periodic cost (benefit)	4.60%	3.60%
Retiree Health and Life [Member] | Salaried Life Insurance [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, benefit obligation	4.00%	4.75%
Discount rate, net periodic cost (benefit)	4.75%	3.90%
Retiree Health and Life [Member] | Hourly Life Insurance [Member]
Expected long term return on assets and to measure the periodic cost
Discount rate, benefit obligation	3.70%	4.40%
Discount rate, net periodic cost (benefit)	4.40%	3.45%

Pension_and_Other_PostRetireme6

Pension and Other Post-Retirement Benefits (Details 4)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Medical Claims [Member]
Review of historical returns
Health care cost trend assumed for next year	7.50%	8.00%
Rate to which the cost trend is expected to decline (the ultimate trend rate)	5.00%	5.00%
Year that rate reaches the ultimate trend rate	2023	2020
Prescription Drugs Claims [Member]
Review of historical returns
Health care cost trend assumed for next year	7.00%	7.00%
Rate to which the cost trend is expected to decline (the ultimate trend rate)	5.00%	5.00%
Year that rate reaches the ultimate trend rate	2023	2020

Pension_and_Other_PostRetireme7

Pension and Other Post-Retirement Benefits (Details 5) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Effect on the other post-retirement benefit cost and obligation
Effect on total of service and interest cost, one percentage point increase	$0.10
Effect on total of service and interest cost, one percentage point decrease	-0.1
Effect on post-retirement benefit obligation, one percentage point increase	2.6
Effect on post-retirement benefit obligation, one percentage point decrease	($2.30)

Pension_and_Other_PostRetireme8

Pension and Other Post-Retirement Benefits (Details 6) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	457
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets
Domestic defined benefit pension plans [Member]
Weighted-average asset allocations of domestic funded pension plans
Target asset allocation percentage	100.00%
Actual plan asset allocations	100.00%	100.00%
Domestic defined benefit pension plans [Member] | Equity Securities [Member]
Weighted-average asset allocations of domestic funded pension plans
Target asset allocation percentage	52.00%
Actual plan asset allocations	51.70%	66.70%
Domestic defined benefit pension plans [Member] | Debt Securities [Member]
Weighted-average asset allocations of domestic funded pension plans
Target asset allocation percentage	44.00%
Actual plan asset allocations	43.90%	27.80%
Domestic defined benefit pension plans [Member] | Real Estate [Member]
Weighted-average asset allocations of domestic funded pension plans
Target asset allocation percentage	4.00%
Actual plan asset allocations	4.30%	5.40%
Domestic defined benefit pension plans [Member] | Cash [Member]
Weighted-average asset allocations of domestic funded pension plans
Target asset allocation percentage	0.00%
Actual plan asset allocations	0.10%	0.10%
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	15.8	447.8
Fair Value, Inputs, Level 1 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets

Pension_and_Other_PostRetireme9

Pension and Other Post-Retirement Benefits (Details 7) (Foreign Pension Plans, Defined Benefit [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Weighted-average asset allocations of its foreign funded pension plan
Target asset allocation percentage	100.00%
Actual plan asset allocations	100.00%	100.00%
Equity Securities [Member]
Weighted-average asset allocations of its foreign funded pension plan
Target asset allocation percentage	36.80%
Actual plan asset allocations	37.70%	38.50%
Debt Securities [Member]
Weighted-average asset allocations of its foreign funded pension plan
Target asset allocation percentage	63.20%
Actual plan asset allocations	62.30%	61.50%

Recovered_Sheet3

Pension and Other Post-Retirement Benefits (Details 8) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fair value of pension plan assets
Assets	$457
Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets	15.8	447.8
Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets
Assets	441.2	25.1
Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets
Assets		422.7
Short-term investment funds [Member]
Fair value of pension plan assets
Assets	0.9
Short-term investment funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets	0.9	1.3
Short-term investment funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets
Assets	0	1.3
Short-term investment funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets
Assets		0
Common stock [Member]
Fair value of pension plan assets
Assets
Common stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets
Common stock [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets
Assets
Common stock [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets
Assets
Common stock collective funds [Member]
Fair value of pension plan assets
Assets	215.2
Common stock collective funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets	0	263
Common stock collective funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets
Assets	215.2	0
Common stock collective funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets
Assets		263
Fixed income collective trust funds [Member]
Fair value of pension plan assets
Assets	208.1
Fixed income collective trust funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets	0	138
Fixed income collective trust funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets
Assets	208.1	0
Fixed income collective trust funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets
Assets		138
Real estate investment funds [Member]
Fair value of pension plan assets
Assets	17.9
Real estate investment funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets	0	21.7
Real estate investment funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value of pension plan assets
Assets	17.9	0
Real estate investment funds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value of pension plan assets
Assets		21.7
UNITED STATES | Common stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets	13.3	21.4
International [Member] | Common stock [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value of pension plan assets
Assets	$1.60	$2.40

Recovered_Sheet4

Pension and Other Post-Retirement Benefits (Details 9) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Qualified Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2015	$28.20
2016	28.3
2017	28.7
2018	29.2
2019	29.6
Years 2020-2024	152.2
Total	296.2
Nonqualified Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2015	2
2016	2.2
2017	2.3
2018	2.3
2019	2.8
Years 2020-2024	15.3
Total	26.9
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2015	3.5
2016	3.4
2017	3.3
2018	3.2
2019	3.1
Years 2020-2024	14
Total	$30.50

Recovered_Sheet5

Pension and Other Post-Retirement Benefits (Details 10) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Multiemployer Plans
Contributions	$8.50		$8.10		$8.10
American Maritime Officers Pension Plan [Member]
Multiemployer Plans
Zone Status	Yellow
Contributions	1.5	[1]	1.4	[1]	1.5	[1]
Collective Bargaining	15-Jan-17
Other Multiemployer Post Retirement Plans [Member]
Multiemployer Plans
Contributions	$7		$6.70		$6.60
[1]	(1)Our contributions represented more than 5% of the total contributions to the plan during each year and no surcharge was imposed for any year. The actuary for the American Maritime Officers Pension Plan certified that the plan is in endangered status (i.e. “yellow zone” as defined by the Pension Protection Act of 2006) for the plan year beginning October 1, 2013, because it has funding or liquidity problems, or both. A rehabilitation plan, as defined by the Employee Retirement Security Act of 1974, was instituted under which certain adjustable benefits were reduced or eliminated, and we are required to contribute at a negotiated rate per day worked by each employee.

Pension_and_Other_Post_Retirem

Pension and Other Post Retirement Benefits (Details Textual) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	Postretirement_Plan
Defined Benefit Plan Disclosure [Line Items]
Number of Postretirement Plans	2
Pension and Other Post Retirement Details (Textual) [Abstract]
Collective bargaining agreement, beginning	2017-01
Defined Benefit Plan, Contributions by Employer	$1.80	$1.60	$1.60
Multiemployer plan contributions	5.00%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of days notice upon which redemptions from real estate funds are available	45 days
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of days notice upon which redemptions from real estate funds are available	60 days
Defined Benefit Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Aggregate accumulated benefit obligation	475.8	426.3
Unrecognized net actuarial loss (gain)	11.3	14.9	9.9
Prior Service Credit	-1	-1	-1
Defined benefit plan, estimated future employer contributions in next fiscal year	6
Pension and Other Post Retirement Details (Textual) [Abstract]
Defined Benefit Plan, Contributions by Employer	2.4	2.4
Other Post-retirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized net actuarial loss (gain)	-0.1	0	-0.1
Prior Service Credit	-0.1	-0.1	-0.1
Pension and Other Post Retirement Details (Textual) [Abstract]
Defined Benefit Plan, Contributions by Employer	$3.90	$3.30

Recovered_Sheet6

Pension and Other Postretirement Benefits (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Contributions by Employer	$1.80	$1.60	$1.60
Defined Benefit Plan, Fair Value of Plan Assets	457
Pension and Other Postretirement Defined Benefit Plans, Liabilities	-86.6	-68.2
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	107.7	78.2	131.1	118.7
Other Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation		40.4
Defined Benefit Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	502.7	442.7	473.8
Defined Benefit Plan, Service Cost	5.9	6.7	5.7
Defined Benefit Plan, Contributions by Employer	2.4	2.4
Unrecognized net actuarial loss (gain)	14.1
Unrecognized prior service credit	-1
Defined Benefit Plan, Interest Cost	20.7	18.4	19.7
Defined Benefit Plan, Actuarial Gain (Loss)	67	-26.8
Defined Benefit Plan, Benefits Paid	-31.2	-30.3
Defined Benefit Plan, Foreign Currency Exchange Rate Gain (Loss)	-2.4	0.9
Defined Benefit Plan, Fair Value of Plan Assets	456.9	447.8	409.1
Defined Benefit Plan, Actual Return on Plan Assets	40.3	65.9
Defined Benefit Plan, Foreign Currency Exchange Rate Changes, Plan Assets	-2.4	0.7
Defined Benefit Plan, Funded Status of Plan	-45.8	5.1
Pension and Other Postretirement Defined Benefit Plans, Liabilities	-45.8	5.1
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Actuarial Loss (Gain) Recognized	170.9	127.6
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Prior Service Credit (Cost) Recognized	-2.1	-3.1
Accumulated other comprehensive loss	168.8	124.5
Defined Benefit Plan, Amounts Recognized in Balance Sheet	123.2	129.6
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	105.4	77.6
Retiree Health and Life [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation	40.8	40.4	48.1
Defined Benefit Plan, Service Cost	0.1	0.2	0.2
Defined Benefit Plan, Contributions by Employer	3.9	3.3
Unrecognized net actuarial loss (gain)	0.1
Unrecognized prior service credit	0.1
Defined Benefit Plan, Interest Cost	1.6	1.6	2
Defined Benefit Plan, Actuarial Gain (Loss)	2.6	-6.2
Defined Benefit Plan, Benefits Paid	-3.9	-3.3
Defined Benefit Plan, Foreign Currency Exchange Rate Gain (Loss)	0	0
Defined Benefit Plan, Fair Value of Plan Assets	0	0	0
Defined Benefit Plan, Actual Return on Plan Assets	0	0
Defined Benefit Plan, Foreign Currency Exchange Rate Changes, Plan Assets	0	0
Defined Benefit Plan, Funded Status of Plan	-40.8	-40.4
Pension and Other Postretirement Defined Benefit Plans, Liabilities	-40.8	-40.4
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Actuarial Loss (Gain) Recognized	3.3	0.6
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Prior Service Credit (Cost) Recognized	0.4	0.4
Accumulated other comprehensive loss	3.7	1
Defined Benefit Plan, Amounts Recognized in Balance Sheet	-37.1	-39.4
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	$2.30	$0.60

Share_Based_Compensation_Weigh

Share Based Compensation - Weighted Average and Assumptions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted average estimated fair value	$18.12	$18.89	$18.48
Quarterly dividend rate	$0.33	$0.30	$0.29
Expected term of stock appreciation rights, in years	4 years 4 months 24 days	4 years 8 months 6 days	4 years 8 months 15 days
Risk-free interest rate	1.30%	0.70%	1.00%
Dividend yield	2.30%	2.60%	2.70%
Expected stock price volatility	30.30%	42.40%	43.30%
Present value of dividends	$5.76	$5.60	$5.37

Share_Based_Compensation_Outst

Share Based Compensation - Outstanding Options and Rights (Details) (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance, Number of Stock Options and Stock Appreciation Rights	1,694
Granted, Number of Stock Options and Stock Appreciation Rights	297
Exercised, Number of Stock Options and Stock Appreciation Rights	467
Forfeitured/Cancelled, Number of Stock Options and Stock Appreciation Rights	33
Expired, Number of Stock Options and Stock Appreciation Rights	1
Ending balance, Number of Stock Options and Stock Appreciation Rights	1,490
Vested and exercisable at end of the year, Number of Stock Options and Stock Appreciation Rights	919
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance, Weighted Average Exercise Price	$36.03
Granted, Weighted Average Exercise Price	$58.50
Exercised, Weighted Average Exercise Price	$37.71
Forfeited/Cancelled, Weighted Average Exercise Price	$50.71
Expired, Weighted Average Exercise Price	$41.02
Ending balance, Weighted Average Exercise Price	$39.65
Vested and exercisable at end of the year	$32.08

Share_Based_Compensation_Aggre

Share Based Compensation - Aggregate Intrinsic Value (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options and Stock Appreciation Rights, Outstanding, Weighted Average Remaining Contractual Term	3 years 8 months 12 days
Stock Options and Stock Appreciation Rights, Vested, Weighted Average Remaining Contractual Term	2 years 7 months 6 days
Stock Options and Stock Appreciation Rights, Exercised, Aggregate Intrinsic Value	$23.80
Stock Options and Stock Appreciation Rights, Outstanding, Aggregate Intrinsic Value	27.5
Stock Option SAR Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options and Stock Appreciation Rights, Exercised, Aggregate Intrinsic Value	$11.80	$6.90	$4.90

ShareBased_Compensation_ShareB

Share-Based Compensation Share-Based Compensation - Restricted Stock and Performance Shares (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, Weighted Average Grant Date Fair Value		$18.89	$18.48
Ending balance, Weighted Average Grant Date Fair Value	$18.12	$18.89	$18.48
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance, Number of Share Units Outstanding	200,050
Granted, Number of Share Units Outstanding	56,020
Vested, Number of Share Units Outstanding	70,986
Forfeited, Number of Share Units Outstanding	-7,874
Ending balance, Number of Share Units Outstanding	177,210
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, Weighted Average Grant Date Fair Value	$41.17
Granted, Weighted Average Grant Date Fair Value	$58.66
Vested, Weighted Average Grant Date Fair Value	$34.77
Forfeited, Weighted Average Grant Date Fair Value	$49.42
Ending balance, Weighted Average Grant Date Fair Value	$48.90
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance, Number of Share Units Outstanding	160,332
Granted, Number of Share Units Outstanding	62,670
Net increase due to estimated performance, Number of Share Units Outstanding	67,392
Vested, Number of Share Units Outstanding	92,958
Forfeited, Number of Share Units Outstanding	-22,367
Ending balance, Number of Share Units Outstanding	175,069
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, Weighted Average Grant Date Fair Value	$44.48
Granted, Weighted Average Grant Date Fair Value	$53.63
Net increase due to estimated performance, Weighted Average Grant Date Fair Value	$47.49
Vested, Weighted Average Grant Date Fair Value	$44.02
Forfeited, Weighted Average Grant Date Fair Value	$46.57
Ending balance, Weighted Average Grant Date Fair Value	$48.95

Share_Based_Compensation_Detai

Share Based Compensation (Details Textual) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for awards	3,500,000
Number of shares available for future issuance	2,400,000
Share-based compensation expense	$14	$13.10	$12.20
Tax benefit from share-based compensation expense	5.3	4.9	4.6
Award vesting period	3 years
Cash proceeds from exercise of stock options		1.2	5.6
Units outstanding	1,490,000	1,694,000
Portion of an award vesting for the 2012 SAR grant	1/3 vesting after each year
Award vesting percentage	33.33%
Stock Options SARs Granted Since 2004 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum granting period for stock option	7 years
Stock Option SAR Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized	14.1
Compensation cost not yet recognized, period for recognition	1 year 8 months 12 days
Restricted Stock and Performance Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Compensation cost not yet recognized	$7.90
Compensation cost not yet recognized, period for recognition	1 year 9 months 18 days
Fair value of restricted stock units and performance shares vested during period	$6,600,000	$7,500,000	$5,600,000
Phantom Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted during period	17,473
Units outstanding	147,962

Income_Taxes_Details

Income Taxes (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent	32.70%	41.20%	18.20%
GATX income taxes on sale of AAE	$0	$23.20	$0
Deferred Tax Liabilities
Book/tax basis difference due to depreciation	963.8	852
Investments in affiliated companies	99.7	93.7
Lease accounting (other than leveraged)	10.5	24.4
Other	0.1	0
Total deferred tax liabilities	1,074.10	970.1
Deferred Tax Assets
Alternative minimum tax credit	9.2	8.4
Federal net operating loss	41.8	8.9
Foreign tax credit	3.6	3.6
Valuation on foreign tax credit	-3.6	-3.6
State net operating loss	28.7	27.1
Valuation on state net operating loss	-11.3	-11.2
Foreign net operating loss	5.8	8.5
Deferred Tax Assets, Valuation Allowance	-0.2	-0.2
Accruals not currently deductible for tax purposes	18.7	14.1
Allowance for losses	1.7	2.2
Pension and post-retirement benefits	32.6	13.3
Other	9.8	7.6
Total deferred tax assets	136.8	78.7
Net deferred tax liabilities	937.3	891.4
Gross liability for unrecognized tax benefits
Beginning balance	5.7	4.7
Reductions due to expiration of the applicable statute of limitations	0.4	0
Reductions due to settlement of audit issues	-0.3	-1
Ending balance	5.6	5.7	4.7
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Amount	0	3.9	13.7
Expiration of the applicable statute of limitations	0.2	-0.6	15.5
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$0	$0	$6.30

Income_Taxes_Details_1

Income Taxes (Details 1) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Provision for Income Taxes, Equity Method Investment	$18.30	$16.50	$2
Equity Method Investment, Summarized Financial Information, Income Tax		15.2	9.2
Income before income taxes
Domestic	137.9	66	80.5
Foreign	93.3	93	63.3
Income before Income Taxes and Share of Affiliates’ Earnings	$231.20	$159	$143.80

Income_Taxes_Details_2

Income Taxes (Details 2) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Equity Method Investment, Summarized Financial Information, Income Tax		$15.20	$9.20
Current
Federal	0.7	1.4	-8.8
State and local	0.6	0	2.5
Current domestic taxes	1.3	1.4	-6.3
Foreign	13	10.5	8
Total current taxes	14.3	11.9	1.7
Deferred
Federal	45	36.6	16
State and local	5.6	5.3	-3.1
Deferred domestic taxes	50.6	41.9	12.9
Foreign	10.8	11.7	11.5
Total deferred taxes	$61.40	$53.60	$24.40

Income_Taxes_Details_3

Income Taxes (Details 3) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of reasons for difference between GATX's effective income tax rate and federal statutory income tax
Income taxes at federal statutory rate	$80.90	$55.60	$50.40
Adjust for effect of:
GATX income taxes on sale of AAE	0	23.2	0
Foreign tax credits	0	-3.9	-13.7
Foreign earnings taxed at lower rates	-8.5	-10.3	-4.1
Tax effect of foreign dividends	0	0	6.3
Expiration of the applicable statute of limitations	0	0	-15.5
Corporate owned life insurance	-0.6	-0.5	-0.3
State income taxes	4.1	1.5	1.9
Other	-0.2	-0.1	1.1
Income taxes	$75.70	$65.50	$26.10
Effective income tax rate	32.70%	41.20%	18.20%

Income_Taxes_Details_Textual

Income Taxes (Details Textual) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Equity Method Investment, Summarized Financial Information, Income Tax		$15.20	$9.20
Effective Income Tax Rate Reconciliation, Percent	32.70%	41.20%	18.20%
Cumulative amount of undistributed earning of foreign subsidiaries	727.7
Alternative minimum tax credit	9.2	8.4
Foreign tax credit	3.6	3.6
Foreign tax credits valuation allowance	3.6	3.6
State net operating loss	28.7	27.1
State net operating loss carryforwards valuation allowance	11.3	11.2
Foreign net operating loss	5.8	8.5
Unrecognized Tax Benefits	5.6	5.7	4.7
Decrease in income tax expenses unrecognized tax benefits if recognized	3.6	3.9
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	0.3	1
Reductions due to expiration of the applicable statute of limitations	0.4	0
Effective Income Tax Rate Reconciliation, Tax Contingency, Domestic, Amount	-0.2	0.6	-15.5
Tax On Gain Of Affiliate Sale	0	-23.2	0
Domestic [Member]
Operating Loss Carryforwards [Line Items]
Amount of U.S. federal tax net operating loss	119.3
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Equity Method Investment, Summarized Financial Information, Income Tax		7.6	4.6
Amount of U.S. federal tax net operating loss	$5.60

Concentrations_Details

Concentrations (Details)	12 Months Ended
	Dec. 31, 2014
Concentration [Abstract]
Concentration Risk, Labor Subject to Collective Bargaining Arrangements	0.4
Multiemployer Plans, Collective-Bargaining Arrangement, Description	three
Canadian
Concentration [Abstract]
Number of service centers	3
Petroleum Industry [Member]
Concentration [Abstract]
Approximate percentage of revenue	24.00%
Chemical Industry [Member]
Concentration [Abstract]
Approximate percentage of revenue	21.00%
Transportation Industry [Member]
Concentration [Abstract]
Approximate percentage of revenue	20.00%
Steel Industry [Member]
Concentration [Abstract]
Approximate percentage of revenue	10.00%
Food/Agriculture [Member]
Concentration [Abstract]
Approximate percentage of revenue	7.00%
Customer Concentration Risk [Member]
Concentration [Abstract]
Approximate percentage of revenue	10.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Concentration [Abstract]
Concentration Risk, Labor Subject to Collective Bargaining Arrangements	0.03
ASC [Member]
Concentration [Abstract]
Concentration Risk, Labor Subject to Collective Bargaining Arrangements	twelve
GERMANY
Concentration [Abstract]
Concentration Risk, Labor Subject to Collective Bargaining Arrangements	one

Commercial_Commitments_Details

Commercial Commitments (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Guarantor Obligations [Line Items]
Guarantor Obligations, Current Carrying Value	$5.10		$6.20
Total commercial commitments	37.6	[1]	49.8	[1]
Asset residual value guarantees [Member]
Guarantor Obligations [Line Items]
Total commercial commitments	0		5.6
Lease payment guarantees [Member]
Guarantor Obligations [Line Items]
Total commercial commitments	28.5		34.8
Performance bonds [Member]
Guarantor Obligations [Line Items]
Total commercial commitments	0.4		0.6
Standby letters of credit [Member]
Guarantor Obligations [Line Items]
Total commercial commitments	$8.70		$8.80
[1]	(1) The carrying value of liabilities on the balance sheet for commercial commitments was $5.1 million at December 31, 2014 and $6.2 million at December 31, 2013. The expirations of these commitments range from 2017 to 2023. We are not aware of any event that would require us to satisfy any of our commitments.

Commercial_Commitments_Details1

Commercial Commitments (Details Textual) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Guarantees [Abstract]
Amount of liability included in recorded value of the company's commitment	$5.10	$6.20
Expiration of commitment range	2017 to 2023

Earnings_Per_Share_Details

Earnings Per Share (Details) (USD $)	3 Months Ended																12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Numerator:
Net income	$58.50		$51.30		$53.10		$42.10		$53.30		$53.80		$35.10		$27.10		$205	$169.30		$137.30
Denominator:
Denominator for basic earnings per share — weighted average shares																	45	46.4		46.8
Effect of dilutive securities:
Equity compensation plans																	0.8	0.7		0.7
Convertible preferred stock																	0	0		0.1
Denominator for diluted earnings per share — adjusted weighted average and assumed conversion																	45.8	47.1		47.6
Basic earnings per share (in dollars per share)	$1.32	[1]	$1.16	[1]	$1.17	[1]	$0.92	[1]	$1.16	[1]	$1.16	[1]	$0.75	[1]	$0.58	[1]	$4.55	$3.64	[1]	$2.93
Diluted earnings per share (in dollars per share)	$1.30	[1]	$1.14	[1]	$1.15	[1]	$0.90	[1]	$1.14	[1]	$1.15	[1]	$0.74	[1]	$0.57	[1]	$4.48	$3.59	[1]	$2.88
[1]	(1)Quarterly earnings per share may not be additive, as per share amounts are computed independently for each quarter and the full year is based on the respective weighted average common shares and common stock equivalents outstanding.

Goodwill_Details

Goodwill (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$86.10	$94.60

Allowance_for_Losses_Details

Allowance for Losses (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Changes in the allowance for possible losses
Beginning balance	$5.20	$4.60
(Reversal) provision for losses	0.8	0.7
Charges to allowance	-0.3	0
Recoveries and other, including foreign exchange adjustments	0	-0.1
Ending balance	$5.70	$5.20

Allowance_for_Losses_Details_T

Allowance for Losses (Details Textual) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Allowance for Losses (Textual) [Abstract]
Allowances for trade receivables	($5.70)	($5.20)	($4.60)
Allowance for Trade Receivables [Member]
Allowance for Losses (Textual) [Abstract]
Allowances for trade receivables	-4.5	-4
Allowances for trade receivables as percentage of rent and other receivables	5.20%	4.90%
Allowance for Finance Leases [Member]
Allowance for Losses (Textual) [Abstract]
Allowances for trade receivables	($1.20)

Other_Assets_and_Other_Liabili1

Other Assets and Other Liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Components of Other Assets reported on the consolidated balance sheets
Inventory	$52	$45.80
Office furniture, fixtures and other equipment, net of accumulated depreciation	34.1	34.9
Derivatives	11.5	6
Deferred financing costs	21.6	18.6
Assets held for sale	6	6.9
Assets held for sale	12.4	12.4
Prepaid pension	0	32.9
Prepaid items	7	10.3
Other	84.4	57.7
Total	$229	$225.50

Other_Assets_and_Other_Liabili2

Other Assets and Other Liabilities (Details 1) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Components of Other Liabilities reported on the consolidated balance sheets
Accrued operating lease expense	$43.40	$48.60
Pension and other post-retirement liabilities	86.6	68.2
Deferred gains on sale-leasebacks	49	53.3
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	3.6	3.9
Environmental reserves	13.8	14.7
Deferred income	5.6	6.7
Derivatives	7.5	3.6
Other Liabilities, Noncurrent	36.6	31.6
Total	$246.10	$230.60

Shareholders_Equity_Details

Shareholders' Equity (Details) (USD $)	12 Months Ended
Share data in Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014
Class of Stock [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Stock Repurchase Program, Authorized Amount		$200,000,000		$250,000,000
Common stock reserved for conversion and incentive plans
Common stock reserved for conversion and incentive plans	6
Stock Repurchased During Period, Shares	1.9	1.4	0
Share-based compensation award plans [Member]
Common stock reserved for conversion and incentive plans
Common stock reserved for conversion and incentive plans	2.5
GATX Corporation 2004 Equity Incentive Compensation Plan [Member]
Common stock reserved for conversion and incentive plans
Common stock reserved for conversion and incentive plans	3.5
Restricted Stock and Performance Share Awards [Member]
Class of Stock [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years

Shareholders_Equity_Details_Te

Shareholders' Equity (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014
Shareholders' Equity (Textual)
Common stock authorized under repurchase program		$200,000,000		$250,000,000
Stock repurchases, Shares	-1,900,000	-1,400,000	0
Payments for stock repurchases	($124,600,000)	($68,600,000)	$0
Common stock, shares authorized	120,000,000	120,000,000
Common Stock, Par or Stated Value Per Share	$0.63	$0.63
Common stock, shares issued	66,600,984	66,349,906
Common stock, shares outstanding	44,198,850	45,868,698
Series A and B $2.50 Cumulative Convertible Preferred Stock [Member]
Shareholders' Equity (Textual)
Preferred stock, shares authorized	5,000,000
Preferred stock, par value	$1
Preferred stock, shares outstanding		15,567
Cumulative annual cash dividend per share on preferred stock	$2.50

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance, Foreign Currency Translation Gain (Loss)	$57.20	$31.40	$6.40
Change in Foreign Currency Translation Gain (Loss)	-79.1	25.8	25
Foreign currency translation gain loss before reclassification adjustment into earnings	0	0	0
Foreign Currency Translation Gain (Loss), Income tax effect	0	0	0
Ending Balance, Foreign Currency Translation Gain (Loss)	-21.9	57.2	31.4
Beginning Balance, Unrealized Gain (Loss) on Securities	0.4	-0.4	-0.6
Change in Unrealized Gain (Loss) on Securities	-0.2	1.4	0.5
Unrealized Gain (Loss) on Securities, Reclassification adjustments into earnings	0	0	-0.4
Unrealized Gain (Loss) on Securities, Income tax effect	0.1	-0.6	0.1
Ending Balance, Unrealized Gain (Loss) on Securities	0.3	0.4	-0.4
Beginning Balance, Unrealized Loss on Derivative Instruments	-22.1	-44.5	-56.2
Change in Unrealized Loss on Derivative Instruments	0.3	22.3	6.2
Unrealized Loss on Derivative Instruments, Reclassification adjustments into earnings	6	6.6	6.5
Unrealized Loss on Derivative Instruments, Income tax effect	-3.3	-6.5	-1
Ending Balance, Unrealized Loss on Derivative Instruments	-19.1	-22.1	-44.5
Beginning Balance, Post-Retirement Benefit Plans	-78.2	-131.1	-118.7
Change in Post-Retirement Benefit Plans	-57.3	71	-28.8
Post-Retirement Benefit Plans, Reclassification adjustments into earnings	10.1	13.8	8.7
Post-Retirement Benefit Plans, Income tax effect	17.7	-31.9	7.7
Ending Balance, Post-Retirement Benefit Plans	-107.7	-78.2	-131.1
Other Comprehensive Income Change in Component	-136.3	120.5	2.9
Reclassification adjustments into earnings, Total	16.1	20.4	14.8
Income tax effect, Total	14.5	-39	6.8
Accumulated other comprehensive income (loss), net of tax	($148.40)	($42.70)	($144.60)	($169.10)

Foreign_Operations_Details

Foreign Operations (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Foreign operations data
Revenues	$401.40	$397.20	$365.80	$286.60	$356.60	$353.20	$338.90	$272.30	$1,451	$1,321	$1,243.20
Identifiable assets	6,937.50				6,549.60				6,937.50	6,549.60	6,055.40
Foreign Operations (Textual) [Abstract]
Maximum percentage of consolidated revenues derive from any individual foreign country									10.00%
Percentage of company's identifiable assets	10.00%								10.00%
Foreign [Member]
Foreign operations data
Revenues									346.2	332.1	279.8
Identifiable assets	2,133.90				2,200.10				2,133.90	2,200.10	1,897.90
United States [Member]
Foreign operations data
Revenues									1,104.80	988.9	963.4
Identifiable assets	$4,803.60				$4,349.50				$4,803.60	$4,349.50	$4,157.50

Legal_Proceedings_and_Other_Co1

Legal Proceedings and Other Contingencies (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Oct. 02, 2013	Dec. 14, 2012	Jun. 29, 2009	Jan. 31, 2015
			Insurance_Provider	Employee		case
				Corporations
Loss Contingencies [Line Items]
Accruals for losses related to probable litigation matters	$1.70
Number of sites for which the Company is involved in environmental remediation	18
Accruals for remediation and restoration	13.8	14.7
Viareggio [Member]
Loss Contingencies [Line Items]
Number of casualties					32
Number of subsidiaries				2
Number of Italian railway companies				4
Number of employees				18
Number of insurers			3
Asbestos - related cases pending against the company and its subsidiaries	90
Legal Fees	$7.80
Number of Maintenance and Supervisory employees				10
Court Proceedings	1
Percentage of coverage held by Liberty Mutual Insurance Europe Limited			25.00%
Asbestos Issue [Member]
Loss Contingencies [Line Items]
New cases filed number	7
Cases dismissed or settled	34
Pending Litigation [Member] | Asbestos Cases [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
Asbestos - related cases pending against the company and its subsidiaries						104
Pending Litigation [Member] | Asbestos Cases [Member] | Subsequent Event [Member] | Jones Act claims [Member]
Loss Contingencies [Line Items]
Asbestos - related cases pending against the company and its subsidiaries						87
Punctured and Ignited [Member] | Viareggio [Member]
Loss Contingencies [Line Items]
number of railcars					1
Overturned [Member] | Viareggio [Member]
Loss Contingencies [Line Items]
number of railcars					5
Derailed [Member] | Viareggio [Member]
Loss Contingencies [Line Items]
number of railcars					14

Financial_Data_of_Business_Seg2

Financial Data of Business Segments (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
									Segment
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment									$18.30	$16.50	$2
Number of business segments									4
Profitability
Lease revenue									1,086.60	975.2	917
Marine operating revenue									286.3	275.1	265.5
Other revenue									78.1	70.7	60.7
Total Revenues	401.4	397.2	365.8	286.6	356.6	353.2	338.9	272.3	1,451	1,321	1,243.20
Maintenance expense									337	294	269.7
Marine operating expense									197.8	189.8	182.4
Depreciation									273.5	255	237.4
Operating lease expense									108.7	129.4	130.2
Other operating expense									28.9	26.1	24.2
Total Expenses									945.9	894.3	843.9
Net gain on asset dispositions									87.2	85.6	79.5
Interest expense, net									-158.4	-166.6	-166.6
Other (expense) income									-13.5	-8.4	-8.2
Share of affiliates' earnings (pre-tax)									67.8	92.3	21.6
Segment profit (loss)									488.2	429.6	325.6
SG&A									189.2	178.3	160.2
Income tax benefit									75.7	65.5	26.1
Net Income	58.5	51.3	53.1	42.1	53.3	53.8	35.1	27.1	205	169.3	137.3
Selected Balance Sheet Data
Investments in affiliated companies	357.7				354.3				357.7	354.3	502
Identifiable assets	6,937.50				6,549.60				6,937.50	6,549.60	6,055.40
Capital Expenditures
Portfolio investments and capital additions									-1,030.50	-859.6	-770
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									5
Profitability
Lease revenue									864.1	758.9	713.9
Marine operating revenue									0	0	0
Other revenue									63.4	58.2	51.4
Total Revenues									927.5	817.1	765.3
Maintenance expense									265.5	228.2	201.4
Marine operating expense									0	0	0
Depreciation									190	176.7	167.7
Operating lease expense									103.7	124.4	126.5
Other operating expense									21.9	18.4	18.5
Total Expenses									581.1	547.7	514.1
Net gain on asset dispositions									72.3	67.7	58.6
Interest expense, net									-98.4	-106	-101.9
Other (expense) income									-7.2	-9.8	-5.1
Share of affiliates' earnings (pre-tax)									7.9	10.3	6.5
Segment profit (loss)									321	231.6	209.3
Selected Balance Sheet Data
Investments in affiliated companies	17.2				31.4				17.2	31.4	46.9
Identifiable assets	4,358.30				3,710.50				4,358.30	3,710.50	3,601.10
Capital Expenditures
Portfolio investments and capital additions									-810.6	-502.4	-465.9
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									2
Profitability
Lease revenue									188.6	180.2	161.2
Marine operating revenue									0	0	0
Other revenue									10.3	8.8	6.5
Total Revenues									198.9	189	167.7
Maintenance expense									45.9	42.9	46.6
Marine operating expense									0	0	0
Depreciation									47.1	43.2	36.1
Operating lease expense									0	0	0
Other operating expense									5.1	5.3	5.1
Total Expenses									98.1	91.4	87.8
Net gain on asset dispositions									6	3.7	1.7
Interest expense, net									-24.7	-23.9	-24.5
Other (expense) income									-3.1	-1.1	-6.1
Share of affiliates' earnings (pre-tax)									-0.3	21.1	-18.3
Segment profit (loss)									78.7	97.4	32.7
Selected Balance Sheet Data
Investments in affiliated companies	1.8				2				1.8	2	77.2
Identifiable assets	1,229.40				1,297.10				1,229.40	1,297.10	1,105.80
Capital Expenditures
Portfolio investments and capital additions									-163.6	-168.5	-200.1
ASC [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									1.5
Profitability
Lease revenue									4.2	4.2	4.3
Marine operating revenue									223	223.5	239.1
Other revenue									0	0	0
Total Revenues									227.2	227.7	243.4
Maintenance expense									25.6	22.9	21.7
Marine operating expense									149.2	151.3	160.3
Depreciation									13.6	12.1	11.9
Operating lease expense									5.2	5.2	3.8
Other operating expense									0	0	-0.3
Total Expenses									193.6	191.5	197.4
Net gain on asset dispositions									-0.5	-1.3	0
Interest expense, net									-5.6	-6.2	-7.1
Other (expense) income									-0.2	0.2	-1.4
Share of affiliates' earnings (pre-tax)									0	0	0
Segment profit (loss)									27.3	28.9	37.5
Selected Balance Sheet Data
Investments in affiliated companies	0				0				0	0	0
Identifiable assets	286.7				271				286.7	271	284.2
Capital Expenditures
Portfolio investments and capital additions									-18.4	-11.2	-12.6
Portfolio Management [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity									3
Profitability
Lease revenue									29.7	31.9	37.6
Marine operating revenue									63.3	51.6	26.4
Other revenue									4.4	3.7	2.8
Total Revenues									97.4	87.2	66.8
Maintenance expense									0	0	0
Marine operating expense									48.6	38.5	22.1
Depreciation									22.8	23	21.7
Operating lease expense									0	0	0.2
Other operating expense									1.9	2.4	0.9
Total Expenses									73.3	63.9	44.9
Net gain on asset dispositions									9.4	15.5	19.2
Interest expense, net									-24.3	-26.7	-27.7
Other (expense) income									-1.2	1.4	3.4
Share of affiliates' earnings (pre-tax)									60.2	60.9	33.4
Segment profit (loss)									68.2	74.4	50.2
Selected Balance Sheet Data
Investments in affiliated companies	338.7				320.9				338.7	320.9	377.9
Identifiable assets	813.3				856.9				813.3	856.9	797.4
Capital Expenditures
Portfolio investments and capital additions									-32.3	-170.5	-83.5
Other [Member]
Profitability
Lease revenue									0	0	0
Marine operating revenue									0	0	0
Other revenue									0	0	0
Total Revenues									0	0	0
Maintenance expense									0	0	0
Marine operating expense									0	0	0
Depreciation									0	0	0
Operating lease expense									-0.2	-0.2	-0.3
Other operating expense									0	0	0
Total Expenses									-0.2	-0.2	-0.3
Net gain on asset dispositions									0	0	0
Interest expense, net									-5.4	-3.8	-5.4
Other (expense) income									-1.8	0.9	1
Share of affiliates' earnings (pre-tax)									0	0	0
Segment profit (loss)									-7	-2.7	-4.1
Selected Balance Sheet Data
Investments in affiliated companies	0				0				0	0	0
Identifiable assets	249.8				414.1				249.8	414.1	266.9
Capital Expenditures
Portfolio investments and capital additions									-5.6	-7	-7.9
Parent [Member]
Profitability
Income tax benefit									$94	$82	$28.10

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (unaudited) (Details) (USD $)	3 Months Ended																12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Selected Quarterly Financial Data (unaudited)
Revenues	$401.40		$397.20		$365.80		$286.60		$356.60		$353.20		$338.90		$272.30		$1,451	$1,321		$1,243.20
Net income	$58.50		$51.30		$53.10		$42.10		$53.30		$53.80		$35.10		$27.10		$205	$169.30		$137.30
Share Data
Basic earnings per share (in dollars per share)	$1.32	[1]	$1.16	[1]	$1.17	[1]	$0.92	[1]	$1.16	[1]	$1.16	[1]	$0.75	[1]	$0.58	[1]	$4.55	$3.64	[1]	$2.93
Diluted earnings per share (in dollars per share)	$1.30	[1]	$1.14	[1]	$1.15	[1]	$0.90	[1]	$1.14	[1]	$1.15	[1]	$0.74	[1]	$0.57	[1]	$4.48	$3.59	[1]	$2.88
[1]	(1)Quarterly earnings per share may not be additive, as per share amounts are computed independently for each quarter and the full year is based on the respective weighted average common shares and common stock equivalents outstanding.

Subsequent_Events_Details

Subsequent Events (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Feb. 03, 2015
In Millions, unless otherwise specified
Subsequent Event [Line Items]
Long-term Debt, Gross	$4,195.80	$3,838.50
Subsequent Event [Member] | Recourse Fixed Rate Debt Unsecured Twenty One [Member]
Subsequent Event [Line Items]
Long-term Debt, Gross			100
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate			2.60%
Subsequent Event [Member] | Recourse Fixed Rate Debt Unsecured Twenty Two [Member]
Subsequent Event [Line Items]
Long-term Debt, Gross			300
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate			3.25%
Subsequent Event [Member] | Recourse Fixed Rate Debt Unsecured Twenty Three [Member]
Subsequent Event [Line Items]
Long-term Debt, Gross			$250
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate			4.50%

Schedule_I_Condensed_Financial1

Schedule I - Condensed Financial Information of Registrant - Balance Sheets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Assets
Cash and cash equivalents	$209.90	$379.70	$234.20	$248.40
Operating assets and facilities, net	5,688	5,070.30
Investments in affiliated companies	357.7	354.3	502
Other assets	229	225.5
Total Assets	6,937.50	6,549.60	6,055.40
Liabilities and Shareholders’ Equity
Accounts payable and accrued expenses	165.9	159.6
Debt	4,274.20	3,871
Other liabilities	246.1	230.6
Total Liabilities	5,623.50	5,152.60
Total Shareholders’ Equity	1,314	1,397	1,244.20
Total Liabilities and Shareholders’ Equity	6,937.50	6,549.60
Parent Company [Member]
Assets
Cash and cash equivalents	162.3	294.6	183.5	208.4
Operating assets and facilities, net	3,397	2,724.30
Investments in affiliated companies	2,199.50	2,197.90
Other assets	396	428.8
Total Assets	6,154.80	5,645.60
Liabilities and Shareholders’ Equity
Accounts payable and accrued expenses	54.9	79.6
Debt	3,821.10	3,249.20
Other liabilities	964.8	919.8
Total Liabilities	4,840.80	4,248.60
Total Shareholders’ Equity	1,314	1,397
Total Liabilities and Shareholders’ Equity	$6,154.80	$5,645.60

Schedule_I_Condensed_Financial2

Schedule I - Condensed Financial Information of Registrant - Statements of Comprehensive Income (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Lease revenue									$1,086.60	$975.20	$917
Other revenue									78.1	70.7	60.7
Total Revenues	401.4	397.2	365.8	286.6	356.6	353.2	338.9	272.3	1,451	1,321	1,243.20
Maintenance expense									337	294	269.7
Depreciation									273.5	255	237.4
Operating lease expense									108.7	129.4	130.2
Other operating expense									28.9	26.1	24.2
Selling, general and administrative									189.2	178.3	160.2
Total Expenses									1,135.10	1,072.60	1,004.10
Net gain on asset dispositions									87.2	85.6	79.5
Interest expense, net									-158.4	-166.6	-166.6
Other (expense) income									-13.5	-8.4	-8.2
Income before Income Taxes and Share of Affiliates’ Earnings									231.2	159	143.8
Income tax benefit									-75.7	-65.5	-26.1
Share of affiliates' earnings (net of tax)									49.5	75.8	19.6
Net Income	58.5	51.3	53.1	42.1	53.3	53.8	35.1	27.1	205	169.3	137.3
Foreign currency translation adjustments									-79.1	25.8	25
Unrealized gain (loss) on securities									-0.1	0.8	0.2
Unrealized gain (loss) on derivative instruments									3	22.4	11.7
Post-retirement benefit plans									-29.5	52.9	-12.4
Other comprehensive income (loss)									-105.7	101.9	24.5
Comprehensive Income									99.3	271.2	161.8
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Lease revenue									669.7	543	504.5
Other revenue									60.2	51.3	43.5
Total Revenues									729.9	594.3	548
Maintenance expense									227.6	176.5	154.8
Depreciation									147.7	131.1	122.2
Operating lease expense									83	89.5	91.6
Other operating expense									17.1	12.7	12
Selling, general and administrative									139.7	131.1	118.4
Total Expenses									615.1	540.9	499
Net gain on asset dispositions									67.9	68.6	59.4
Interest expense, net									-66.7	-63.7	-65.4
Other (expense) income									2.5	-7	-4.4
Income before Income Taxes and Share of Affiliates’ Earnings									118.5	51.3	38.6
Income tax benefit									-41.7	-10.7	1
Share of affiliates' earnings (net of tax)									128.2	128.7	97.7
Net Income									205	169.3	137.3
Foreign currency translation adjustments									-79.1	25.8	25
Unrealized gain (loss) on securities									-0.1	0.8	0.2
Unrealized gain (loss) on derivative instruments									3	22.4	11.7
Post-retirement benefit plans									-29.5	52.9	-12.4
Other comprehensive income (loss)									-105.7	101.9	24.5
Comprehensive Income									$99.30	$271.20	$161.80

Schedule_I_Condensed_Financial3

Schedule I - Condensed Financial Information of Registrant - Statements of Cash Flows (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net cash provided by operating activities	$449.20	$400.70	$370.20
Investing Activities
Purchases of leased-in assets	-150.5	-61.4	-1.3
Proceeds from sale-leasebacks	0	90.7	104.9
Portfolio proceeds and other	264	385.3	288.9
Net cash used in investing activities	-878.5	-403.2	-343.6
Financing Activities
Repayments of debt (original maturities longer than 90 days)	-819.8	-602.8	-671.2
Net increase (decrease) in debt with original maturities of 90 days or less	50	-251.3	243.3
Proceeds from issuances of debt (original maturities longer than 90 days)	1,223	1,132.20	445.2
Stock repurchases	-124.6	-68.6	0
Dividends	-62	-60.5	-58.8
Net cash (used in) provided by financing activities	262.2	149.1	-39.9
Net (decrease) increase in cash and cash equivalents during the period	-169.8	145.5	-14.2
Cash and Cash Equivalents at beginning of period	379.7	234.2	248.4
Cash and Cash Equivalents at end of period	209.9	379.7	234.2
Parent Company [Member]
Operating Activities
Net cash provided by operating activities	219.5	104.3	269.6
Investing Activities
Capital additions	748.1	513.5	444.6
Purchases of leased-in assets	-150.5	-61.4	-1.4
Proceeds from sale-leasebacks	0	90.7	104.9
Portfolio proceeds and other	169.5	320.7	136.6
Net cash used in investing activities	-729.1	-163.5	-204.5
Financing Activities
Repayments of debt (original maturities longer than 90 days)	-692.2	-483.8	-603.7
Net increase (decrease) in debt with original maturities of 90 days or less	69	-185	185
Proceeds from issuances of debt (original maturities longer than 90 days)	1,188.70	967	381.4
Stock repurchases	-124.6	-68.6	0
Dividends	-62	-60.5	-57.7
Other	-1.6	1.2	5
Net cash (used in) provided by financing activities	377.3	170.3	-90
Net (decrease) increase in cash and cash equivalents during the period	-132.3	111.1	-24.9
Cash and Cash Equivalents at beginning of period	294.6	183.5	208.4
Cash and Cash Equivalents at end of period	$162.30	$294.60	$183.50