Acquisitions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		6 Months Ended							6 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2013 Acquisitions	Jun. 30, 2012	Jun. 30, 2013 Minimum [Member]	Jun. 30, 2013 Maximum [Member]	Feb. 29, 2012 Acquisition Yokogawa-ORC [Member]	Jun. 30, 2013 Purchase Consideration for Acquisitions During the Period [Member]	Jun. 30, 2012 Purchase Consideration for Acquisitions During the Period [Member]	Jun. 30, 2013 Released Cash Held in Escrow [Member]	Jun. 30, 2013 Current Year Acquisitions [Member]	Jun. 30, 2013 Current Year Acquisitions [Member] Minimum [Member]	Jun. 30, 2013 Current Year Acquisitions [Member] Maximum [Member]	Jun. 30, 2013 Prior Years Acquisitions [Member]	Jun. 30, 2012 Prior Years Acquisitions [Member]	Jun. 30, 2013 Consulting [Member]	Jun. 30, 2013 Risk and Insurance Services [Member] Acquisitions	Dec. 31, 2012 Risk and Insurance Services [Member] Acquisitions	Dec. 31, 2012 Consulting [Member] Acquisitions
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions)	2														2	12	3
Total Consideration	$ 109	$ 183							$ 109
Cash						95	103	62	95
Estimated fair value of deferred/contingent consideration	(14)	(18)				14	18		14			(5)
Revenue target period (in years)			2 years	4 years						2 years	4 years
Deferred purchase consideration												3	61
Business combination remaining percent acquired					49.00%
Subsequent Event, Amount														$ 30