Represents gain (loss) from equity in earnings of joint ventures due to the change in control during the period.

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Represents the after tax amount of gain (loss) from equity in earnings of joint ventures due to the change in control during the period.

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Represents the fair value portion of investments accounted under the equity method excluding control premium.

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Represents the entity's proportionate share for the period of the net income (loss) of its other joint ventures to which the equity method of accounting is applied. Other joint ventures are those which have their own employees and operating expenses, and to which the entity generally makes a capital contribution.

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Represents the entity's proportionate share for the period of the net income (loss) of its pass through joint ventures to which the equity method of accounting is applied. Pass through joint ventures are those in which the entities' own employees perform work for the joint venture, which is then billed to a third-party customer by the joint venture.

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Represents the number of employees in certain joint ventures of the entity.

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Represents the number of partners that are required to form joint ventures for specific projects.

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold or consumed after one year or beyond the normal operating cycle, if longer.

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Total costs related to services rendered by an entity during the reporting period.

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Includes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership.

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Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.

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Amount of liabilities and equity items, including the portion of equity attributable to noncontrolling interests, if any.

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Total obligations incurred as part of normal operations that are expected to be paid during the following twelve months or within one business cycle, if longer.

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Amount of obligation due after one year or beyond the normal operating cycle, if longer.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest).

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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Aggregate revenue during the period from services rendered in the normal course of business, after deducting allowances and discounts.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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Joint Ventures and Variable Interest Entities (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended
	Mar. 31, 2015 item	Mar. 31, 2014	Mar. 31, 2015 item	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2014
Financial information
Number of employees in some joint ventures	0		0
Current assets	$ 5,985,183,000us-gaap_AssetsCurrent		$ 5,985,183,000us-gaap_AssetsCurrent			$ 3,434,113,000us-gaap_AssetsCurrent
TOTAL ASSETS	14,016,005,000us-gaap_Assets		14,016,005,000us-gaap_Assets			6,123,377,000us-gaap_Assets
Current liabilities	4,461,104,000us-gaap_LiabilitiesCurrent		4,461,104,000us-gaap_LiabilitiesCurrent			2,455,769,000us-gaap_LiabilitiesCurrent
TOTAL LIABILITIES	10,295,160,000us-gaap_Liabilities		10,295,160,000us-gaap_Liabilities			3,850,897,000us-gaap_Liabilities
Total AECOM equity	3,429,567,000us-gaap_StockholdersEquity		3,429,567,000us-gaap_StockholdersEquity			2,186,517,000us-gaap_StockholdersEquity
Noncontrolling interests	291,278,000us-gaap_MinorityInterest		291,278,000us-gaap_MinorityInterest			85,963,000us-gaap_MinorityInterest
TOTAL STOCKHOLDERS' EQUITY	3,720,845,000		3,720,845,000			2,272,480,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	14,016,005,000		14,016,005,000			6,123,377,000
AECOM's investment in joint ventures	336,221,000		336,221,000			142,901,000
Gross Profit	103,312,000us-gaap_GrossProfit	87,407,000us-gaap_GrossProfit	238,042,000us-gaap_GrossProfit	165,605,000us-gaap_GrossProfit
Joint ventures summarized financial information
Revenue	4,506,197,000us-gaap_SalesRevenueServicesNet	1,872,224,000us-gaap_SalesRevenueServicesNet	8,716,665,000us-gaap_SalesRevenueServicesNet	3,826,099,000us-gaap_SalesRevenueServicesNet
Cost of revenue.	4,402,885,000us-gaap_CostOfServices	1,784,817,000us-gaap_CostOfServices	8,478,623,000us-gaap_CostOfServices	3,660,494,000us-gaap_CostOfServices
Gross Profit	103,312,000us-gaap_GrossProfit	87,407,000us-gaap_GrossProfit	238,042,000us-gaap_GrossProfit	165,605,000us-gaap_GrossProfit
Net income (loss)	20,604,000us-gaap_ProfitLoss	42,496,000us-gaap_ProfitLoss	(97,463,000)us-gaap_ProfitLoss	99,037,000us-gaap_ProfitLoss
Summary of AECOM's equity in earnings of unconsolidated joint ventures:
Total	24,628,000	7,436,000	48,552,000	43,519,000
Minimum
Financial information
Number of partners required to form joint ventures	2		2
Consolidated Joint Ventures
Financial information
Current assets	677,900,000		677,900,000			314,100,000
Non-current assets	251,200,000		251,200,000			106,200,000
TOTAL ASSETS	929,100,000		929,100,000			420,300,000
Current liabilities	375,700,000		375,700,000			229,100,000
Non-current liabilities	7,900,000		7,900,000
TOTAL LIABILITIES	383,600,000		383,600,000			229,100,000
Total AECOM equity	264,800,000		264,800,000			116,600,000
Noncontrolling interests	280,700,000		280,700,000			74,600,000
TOTAL STOCKHOLDERS' EQUITY	545,500,000		545,500,000			191,200,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	929,100,000		929,100,000			420,300,000
Joint ventures summarized financial information
Revenue			1,188,900,000	229,300,000
Consolidated Joint Venture During Quarter Ended 03312014
Financial information
TOTAL ASSETS	201,000,000		201,000,000
TOTAL LIABILITIES	48,000,000		48,000,000
Equity in earnings of unconsolidated joint ventures
Gain (loss) from equity in earnings of joint ventures due to the change in control					37,400,000
Gain (loss) from equity in earnings of joint ventures due to the change in control, net of tax					23,400,000
Fair value of the previously held equity interest, excluding control premium	58,000,000		58,000,000
Unconsolidated Joint Ventures
Financial information
Current assets	1,159,400,000		1,159,400,000			539,600,000
Non-current assets	524,000,000		524,000,000			273,700,000
TOTAL ASSETS	1,683,400,000		1,683,400,000			813,300,000
Current liabilities	870,800,000		870,800,000			397,900,000
Non-current liabilities	121,100,000		121,100,000			91,000,000
TOTAL LIABILITIES	991,900,000		991,900,000			488,900,000
TOTAL STOCKHOLDERS' EQUITY	691,500,000		691,500,000			324,400,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,683,400,000		1,683,400,000			813,300,000
AECOM's investment in joint ventures	336,200,000		336,200,000			142,900,000
Gross Profit			116,600,000	34,300,000
Joint ventures summarized financial information
Revenue			2,175,600,000	991,700,000
Cost of revenue.			2,059,000,000	957,400,000
Gross Profit			116,600,000	34,300,000
Net income (loss)			104,200,000	34,300,000
Summary of AECOM's equity in earnings of unconsolidated joint ventures:
Pass through joint ventures			13,400,000	3,200,000
Other joint ventures			35,200,000	40,300,000
Total			$ 48,600,000	$ 43,500,000