Acquisitions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		3 Months Ended					3 Months Ended			12 Months Ended
	Mar. 31, 2013 Acquisitions	Mar. 31, 2012	Mar. 31, 2013 Minimum [Member]	Mar. 31, 2013 Maximum [Member]	Feb. 29, 2012 Acquisition Yokogawa-ORC [Member]	Mar. 31, 2012 Purchase Consideration for Acquisitions During the Period [Member]	Mar. 31, 2013 Released Cash Held in Escrow [Member]	Mar. 31, 2013 Current Year Acquisitions [Member] Minimum [Member]	Mar. 31, 2013 Current Year Acquisitions [Member] Maximum [Member]	Mar. 31, 2012 Prior Years Acquisitions [Member]	Dec. 31, 2012 Risk and Insurance Services [Member] Acquisitions	Dec. 31, 2012 Consulting [Member] Acquisitions
Number of acquisitions made (in acquisitions)	0										12	3
Business combination remaining percent acquired					49.00%
Total Consideration		$ 148
Cash						73	62
Contingent consideration	0	(13)				13
Revenue target period (in years)			2 years	4 years				2 years	4 years
Deferred purchase consideration										$ 20