Integration and Restructuring Costs (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	$ 22	$ 78	$ 51
Liability balance	124	170	181	211
Payments for restructuring	65	88	82
Risk and Insurance Services Segment [Member] | Acquisition Related [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	7
Consulting Segment [Member] | Acquisition Related [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	2
Corporate Segment [Member] | Acquisition Related [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring actions costs	$ 13