Integration and Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	$ 28	$ 12	$ 22
Liability balance	93	92	124	$ 170
Payments for restructuring	28	$ 43	$ 68
Operating Segments | Risk and Insurance Services Segment | Acquisition Related
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	8
Operating Segments | Consulting Segment | Acquisition Related
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	8
Corporate, Non-Segment | Acquisition Related
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	$ 12