Salaries and Benefits Expense (Details) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2011
Severance liability
Beginning Balance		$ 0
Severance costs accrued	9	55
Ending Balance	26	26
Employee Severance [Member]
Severance liability
Severance costs accrued		55
Cash payments		(29)
Foreign exchange		$ 0

Cash outflows for payments of postemployment benefits (such as severance pay and health insurance benefits) recognized during the period. Postemployment benefits are benefits paid to employees after employment but before retirement.

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of foreign currency translation adjustment increasing or decreasing the accrual for a specified type of restructuring cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 95-3

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 5
-Section P
-Subsection 3, 4

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 146

+ Details

Name:	us-gaap_RestructuringReserveTranslationAdjustment
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Liability for amount due employees, in addition to wages and any other money that employers owe employees, when their employment ends through a layoff or other termination. For example, a company may provide involuntarily terminated employees with a lump sum payment equal to one week's salary for every year of employment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 112
-Paragraph 1

+ Details

Name:	us-gaap_SupplementalUnemploymentBenefitsSeveranceBenefits
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Severance costs incurred as part of the Company's business operational review.

+ Details

Name:	wsh_OperationalReviewSeveranceCosts
Namespace Prefix:	wsh
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration