Acquisitions (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended					3 Months Ended	9 Months Ended					12 Months Ended
	Mar. 31, 2013	Sep. 30, 2013 acquisition	Sep. 30, 2012	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Maximum [Member]	Feb. 29, 2012 Acquisition Yokogawa-ORC [Member]	Sep. 30, 2013 Current Fiscal Period Acquisitions [Member]	Sep. 30, 2013 Current Fiscal Period Acquisitions [Member]	Sep. 30, 2013 Current Fiscal Period Acquisitions [Member] Minimum [Member]	Sep. 30, 2013 Current Fiscal Period Acquisitions [Member] Maximum [Member]	Sep. 30, 2013 Prior Fiscal Periods Acquisitions [Member]	Sep. 30, 2012 Prior Fiscal Periods Acquisitions [Member]	Dec. 31, 2012 Marsh Insurance Group [Member] acquisition	Dec. 31, 2012 Mercer Consulting Group [Member] acquisition
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions)		6											12	3
Business combination remaining percent acquired						49.00%
Total Consideration		$ 156	$ 205					$ 156
Cash		119	124					119
Estimated fair value of deferred/contingent consideration		37	19					37
Revenue target period (in years)				2 years	4 years				2 years	4 years
Cash held in escrow related to acquisition	62
Deferred purchase consideration											8
Revenue related to acquisitions							13	13
Operating income related to acquisitions							0	0
Deferred purchase consideration from prior years' acquisitions		$ 4	$ 51								$ 4	$ 51