Condensed Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Revenues	$ 2,581,009	$ 2,305,723	$ 7,520,451	$ 6,487,701
Cost of Services, Excluding Depreciation, Depletion, and Amortization	1,569,828	1,382,336	4,501,734	3,854,314
Operating expenses:
Selling, general and administrative expenses	506,019	443,376	1,474,399	1,277,106
Depreciation and amortization expense	47,649	42,652	138,848	126,212
Income from operations	457,513	437,359	1,405,470	1,230,069
Other income (expense), net:
Interest income	17,201	10,696	44,838	37,023
Foreign currency exchange gains (losses), net	(11,222)	(9,189)	(13,191)	(32,014)
Other, net	247	332	1,648	1,700
Total other income (expense), net	6,226	1,839	33,295	6,709
Income before provision for income taxes	463,739	439,198	1,438,765	1,236,778
Provision for income taxes	108,115	119,571	362,355	332,532
Net income	$ 355,624	$ 319,627	$ 1,076,410	$ 904,246
Basic earnings per share (in dollars per share)	$ 0.58	$ 0.53	$ 1.77	$ 1.50
Diluted earnings per share (in dollars per share)	$ 0.58	$ 0.53	$ 1.76	$ 1.48
Weighted average number of common shares outstanding - Basic	608,070	603,265	607,894	603,437
Dilutive effect of shares issuable under stock-based compensation plans	4,053	5,284	4,500	5,827
Weighted average number of common shares outstanding - Diluted	612,123	608,549	612,394	609,264