Fiduciary Assets And Liabilities (Details) (USD $)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Risk and Insurance Services [Member]	Mar. 31, 2012 Risk and Insurance Services [Member]	Mar. 31, 2013 Consulting [Member]	Mar. 31, 2012 Consulting [Member]
Interest on fiduciary funds			$ 8,000,000	$ 11,000,000	$ 1,000,000	$ 1,000,000
Net uncollected premiums and claims receivable and payable	10,100,000,000	9,100,000,000
Assets in trusts or funds for management or trustee fee					$ 17,000,000,000