Goodwill And Other Intangibles (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010		Dec. 31, 2009
Segment Reporting Information [Line Items]
Goodwill impairment charge				$ 315
Goodwill impairment related to discontinued operations				315
Goodwill acquired	124	502
Finite lived assets amortization expense	65	50		26
Goodwill	6,562	6,420	[1]	5,990	[1]
Risk and Insurance Services [Member]
Segment Reporting Information [Line Items]
Goodwill acquired	76
Goodwill	4,500
Consulting [Member]
Segment Reporting Information [Line Items]
Goodwill acquired	48
Goodwill	$ 2,100

[1] Amounts in 2010 exclude goodwill and accumulated impairment losses related to Kroll, which were reclassified to discontinued operations.