Acquisitions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended						3 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Sep. 30, 2010	Jun. 30, 2012	Jun. 30, 2011	Feb. 29, 2012 Acquisition Yokogawa-ORC [Member]	Jun. 30, 2012 Business Acquisition [Member]	Jun. 30, 2012 Business Acquisition [Member]	Jun. 30, 2012 Purchase Consideration for Acquisitions During the Period [Member]	Jun. 30, 2011 Purchase Consideration for Acquisitions During the Period [Member]	Jun. 30, 2012 Cash [Member]	Jun. 30, 2012 Released Cash Held in Escrow [Member]	Jun. 30, 2011 Prior Years Acquisitions [Member]	Jun. 30, 2011 Minority Interest Acquired [Member]	Jun. 30, 2012 Risk and Insurance Services [Member] Acquisitions	Dec. 31, 2011 Risk and Insurance Services [Member] Acquisitions	Jun. 30, 2012 Consulting [Member] Acquisitions	Dec. 31, 2011 Consulting [Member] Acquisitions
Number of acquisitions made (in acquisitions)														5	7	3	5
Business combination remaining percent acquired					49.00%
Total Consideration	$ 183		$ 183	$ 114				$ 183					$ 8
Adjustments to Additional Paid in Capital, Other													2
Cash	165		165						101	103	62
Contingent consideration	18		18	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								61	13			15
Revenue related to acquisitions	3,030	2,974	6,092	5,908		24	45
Net operating income related to acquisitions	$ 340	$ 289	$ 695	$ 605		$ 6	$ 8