Segment Information (Details) (USD $)	3 Months Ended										12 Months Ended
	Jun. 30, 2012		Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2010
Segment Reporting Information [Line Items]
Revenue (net of reimbursable expenses)											$ 3,314,434,000		$ 3,141,275,000		$ 2,317,487,000
Net operating income											970,913,000		887,894,000		570,949,000
Depreciation and amortization											39,162,000		35,469,000		41,765,000
Receivables	875,773,000	[1]				748,122,000	[1]				875,773,000	[1]	748,122,000	[1]	640,121,000	[1]
Revenues:
Total segment revenue											3,314,434,000		3,141,275,000		2,317,487,000
Reimbursable expenses and other											103,302,000		118,176,000		70,342,000
Revenue	826,159,000		901,516,000	879,710,000	810,351,000	851,265,000		866,081,000	790,664,000	751,441,000	3,417,736,000		3,259,451,000		2,387,829,000
Net operating income:
Total segment net operating income											970,913,000		887,894,000		570,949,000
Differences in allocation methods											(7,078,000)	[2]	18,934,000	[2]	7,012,000	[2]
Amortization of intangibles											(65,575,000)		(51,989,000)		(31,280,000)
Transaction and integration expenses											(86,130,000)		(100,535,000)		(87,644,000)
Stock-based compensation											(42,308,000)	[3]	(76,000,000)	[3]	(48,006,000)	[3]
Discretionary compensation											(318,455,000)		(337,694,000)		(236,154,000)
Change in accounting method for pension											(2,963,000)	[4]	0		0
Other, net											(48,488,000)		(27,447,000)		(10,432,000)
Income from operations	96,890,000		108,883,000	99,134,000	95,009,000	89,647,000		102,273,000	62,053,000	59,190,000	399,916,000		313,163,000		164,445,000
Depreciation and Amortization Expense
Total segment expense											39,162,000		35,469,000		41,765,000
Intangible asset amortization, not allocated to segments											65,575,000		51,989,000		31,280,000
Information technology and other											48,154,000		43,117,000		28,039,000
Total depreciation and amortization expense											152,891,000		130,575,000		101,084,000
Receivables
Total segment receivables - billed and unbilled	875,773,000	[1]				748,122,000	[1]				875,773,000	[1]	748,122,000	[1]	640,121,000	[1]
Valuation differences and other	8,578,000					30,808,000					8,578,000		30,808,000		(2,607,000)
Total billed and unbilled receivables	884,351,000					778,930,000					884,351,000		778,930,000		637,514,000
Assets Not Reported By Segments	4,472,627,000					4,320,020,000					4,472,627,000		4,320,020,000		3,936,103,000
Total Assets	5,356,978,000					5,098,950,000					5,356,978,000		5,098,950,000		4,573,617,000
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in accounting method for pension, net impact to the quarter											(2,963,000)	[4]	0		0
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-Lived Assets	3,440,090,000					3,207,325,000					3,440,090,000		3,207,325,000		2,733,463,000
North America
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues											1,858,521,000		1,865,299,000		1,325,876,000
Long-Lived Assets	2,263,592,000					1,536,071,000					2,263,592,000		1,536,071,000		1,331,241,000
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues											1,267,585,000		1,158,567,000		888,076,000
Long-Lived Assets	1,110,367,000					1,607,604,000					1,110,367,000		1,607,604,000		1,352,990,000
Rest of World
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues											291,630,000		235,585,000		173,877,000
Long-Lived Assets	66,131,000					63,650,000					66,131,000		63,650,000		49,232,000
Pension Change In Accounting Principle [Member]
Net operating income:
Change in accounting method for pension											(3,000,000)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in accounting method for pension, gross impact				9,500,000							(6,200,000)
Change in accounting method for pension, offset for the period	6,600,000										(3,200,000)
Change in accounting method for pension, net impact to the quarter											(3,000,000)
Total [Member]
Segment Reporting Information [Line Items]
Revenue (net of reimbursable expenses)											3,314,434,000		3,141,275,000		2,317,487,000
Net operating income											970,913,000		887,894,000		570,949,000
Depreciation and amortization											39,162,000		35,469,000		41,765,000
Receivables	875,773,000					748,122,000					875,773,000		748,122,000		640,121,000
Revenues:
Total segment revenue											3,314,434,000		3,141,275,000		2,317,487,000
Net operating income:
Total segment net operating income											970,913,000		887,894,000		570,949,000
Depreciation and Amortization Expense
Total segment expense											39,162,000		35,469,000		41,765,000
Receivables
Total segment receivables - billed and unbilled	875,773,000					748,122,000					875,773,000		748,122,000		640,121,000
Benefits [Member]
Segment Reporting Information [Line Items]
Revenue (net of reimbursable expenses)											1,922,689,000		1,857,047,000		1,470,817,000
Net operating income											646,418,000		609,133,000		441,159,000
Depreciation and amortization											23,219,000		21,888,000		26,509,000
Receivables	548,629,000					460,492,000					548,629,000		460,492,000		400,169,000
Revenues:
Total segment revenue											1,922,689,000		1,857,047,000		1,470,817,000
Net operating income:
Total segment net operating income											646,418,000		609,133,000		441,159,000
Depreciation and Amortization Expense
Total segment expense											23,219,000		21,888,000		26,509,000
Receivables
Total segment receivables - billed and unbilled	548,629,000					460,492,000					548,629,000		460,492,000		400,169,000
Risk And Financial Services [Member]
Segment Reporting Information [Line Items]
Revenue (net of reimbursable expenses)											817,591,000		740,721,000		494,961,000
Net operating income											211,601,000		181,970,000		112,373,000
Depreciation and amortization											8,443,000		6,239,000		6,520,000
Receivables	185,950,000					167,709,000					185,950,000		167,709,000		132,487,000
Revenues:
Total segment revenue											817,591,000		740,721,000		494,961,000
Net operating income:
Total segment net operating income											211,601,000		181,970,000		112,373,000
Depreciation and Amortization Expense
Total segment expense											8,443,000		6,239,000		6,520,000
Receivables
Total segment receivables - billed and unbilled	185,950,000					167,709,000					185,950,000		167,709,000		132,487,000
Talent And Rewards [Member]
Segment Reporting Information [Line Items]
Revenue (net of reimbursable expenses)											570,537,000		543,507,000		351,709,000
Net operating income											113,608,000		96,791,000		17,417,000
Depreciation and amortization											7,401,000		7,342,000		8,736,000
Receivables	140,575,000					119,921,000					140,575,000		119,921,000		107,465,000
Revenues:
Total segment revenue											570,537,000		543,507,000		351,709,000
Net operating income:
Total segment net operating income											113,608,000		96,791,000		17,417,000
Depreciation and Amortization Expense
Total segment expense											7,401,000		7,342,000		8,736,000
Receivables
Total segment receivables - billed and unbilled	140,575,000					119,921,000					140,575,000		119,921,000		107,465,000
Exchange Solutions [Member]
Segment Reporting Information [Line Items]
Revenue (net of reimbursable expenses)											3,617,000		0		0
Net operating income											(714,000)		0		0
Depreciation and amortization											99,000		0		0
Receivables	619,000					0					619,000		0		0
Revenues:
Total segment revenue											3,617,000		0		0
Net operating income:
Total segment net operating income											(714,000)		0		0
Depreciation and Amortization Expense
Total segment expense											99,000		0		0
Receivables
Total segment receivables - billed and unbilled	$ 619,000					$ 0					$ 619,000		$ 0		$ 0

[1] Total segment receivables, which reflect the receivable balances used by management to make business decisions, are included for management reporting purposes net of deferred revenue.

[2] Depreciation, general and administrative, pension, and medical costs are allocated to our segments based on budgeted expenses determined at the beginning of the fiscal year as management believes that these costs are largely uncontrollable to the segment. To the extent that the actual expense base upon which allocations are made differs from the forecast/budget amount, a reconciling item will be created between internally allocated expenses and the actual expense that we report for GAAP purposes.

[3] Stock-based compensation excludes RSUs granted in conjunction with our performance bonus, which are included in discretionary compensation.

[4] The Company had a net impact of $3.0 million during the year as a result of the cumulative effect of the change in accounting method (see Note 1) of $6.2 million offset by a reduction in net periodic cost of $3.2 million