Fiduciary Assets And Liabilities (Details) (USD $)	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Risk and Insurance Services [Member]	Mar. 31, 2011 Risk and Insurance Services [Member]	Mar. 31, 2012 Consulting [Member]	Mar. 31, 2011 Consulting [Member]
Interest on fiduciary funds			$ 11,000,000	$ 12,000,000	$ 1,000,000	$ 1,000,000
Fixed income securities in fiduciary assets	42,000,000	62,000,000
Unrealized gains, net of tax	0	2,000,000
Net uncollected premiums and claims receivable and payable	10,000,000,000	9,000,000,000
Assets in trusts or funds for management or trustee fee					$ 16,000,000,000