Comprehensive Income (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Comprehensive Income, Net of Tax, Attributable to Parent [Abstract]
NET (LOSS) INCOME	$ 89	$ 91	$ 131	$ 302	[1]
Comprehensive income
Foreign currency translation adjustment (net of tax of $nil, $nil, $nil and $nil)	25	(29)	65	(35)
Pension funding adjustment (net of tax of $nil million, $(2) million, $(1) million and $(5) million)	0	6	(5)	12
Net loss on derivative instruments (net of tax of $1 million, $ (2) million, $ 3 million and $ (2) million)	(4)	7	(7)	7
Other comprehensive income (net of tax of $1 million, $(4) million, $2 million and $(7) million)	21	(16)	53	(16)
Comprehensive income, total	110	75	184	286
Noncontrolling interest	(4)	(2)	(12)	(9)
Comprehensive income attributable to Willis Group Holdings	$ 106	$ 73	$ 172	$ 277

[1] The 2010 Unaudited Condensed Consolidated Statement of Cash Flows has been recast to conform to the new balance sheet presentation. See Note 2 - Basis of Presentation and Significant Accounting Policies for details.