Acquisitions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			3 Months Ended						3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Feb. 29, 2012 Acquisition Yokogawa-ORC [Member]	Mar. 31, 2012 Business Acquisition [Member]	Mar. 31, 2012 Purchase Consideration for Acquisitions During the Period [Member]	Mar. 31, 2011 Purchase Consideration for Acquisitions During the Period [Member]	Mar. 31, 2012 Cash [Member]	Mar. 31, 2012 Released Cash Held in Escrow [Member]	Mar. 31, 2011 Prior Years Acquisitions [Member]	Mar. 31, 2012 Risk and Insurance Services [Member] Acquisitions	Mar. 31, 2011 Risk and Insurance Services [Member] Acquisitions	Mar. 31, 2012 Consulting [Member] Acquisitions	Mar. 31, 2011 Consulting [Member] Acquisitions
Number of acquisitions made (in acquisitions)										3	7	3	5
Business combination remaining percent acquired			49.00%
Total Consideration	$ 148	$ 106			$ 148
Cash	135					93	73	62
Contingent consideration	(13)	(13)				13
Revenue target period, in years	two to four years
Revenue target period minimum (in years)	2 years
Revenue target period maximum (in years)	4 years
Deferred purchase consideration					20	13			14
Revenue related to acquisitions	3,058	2,929		20
Net operating income related to acquisitions	$ 355	$ 315		$ 1