Derivative Financial Instruments and Hedging Activities (Details Textuals) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 2
Notional amount of interest rate swaps	350
Debt Instrument, Maturity Date	Jul. 15, 2015
Senior Notes [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt instrument, face amount	2,050
Senior Notes Due 2015 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt instrument, face amount	350
Debt Instrument, Interest Rate, Stated Percentage	5.625%
Senior Notes Due 2016 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt instrument, face amount	300
Senior Notes Due 2017 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt instrument, face amount	600
Senior Notes Due 2019 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt instrument, face amount	300
Senior Notes Due 2021 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt instrument, face amount	500
Five Year Term Loan Facility [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Operations financed by 5-year term loan facility	356
Debt Instrument Interest	LIBOR plus 2.250%
Maturity period of term loan	5-years
Revolving credit facility [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Revolving credit facilities available	520
Revolving $300 million credit facility [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt Instrument Interest	LIBOR plus 2.250%
Line of Credit Facility, Amount Outstanding	0
Revolving credit facilities available	300
Revolving $200 million credit facility [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Debt Instrument Interest	LIBOR plus either 1.750% or 2.750%
Line of Credit Facility, Amount Outstanding	0
Revolving credit facilities available	200
Revolving $20 million credit facility [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Line of Credit Facility, Amount Outstanding	0
Revolving credit facilities available	$ 20

The estimated net amount of existing gains (losses) on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 45
-Subparagraph b(2)

+ Details

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Balance Type:	credit
Period Type:	duration

- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 21
-Paragraph 16, 20

+ Details

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

- Definition

Interest rate stated in the contractual debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

+ Details

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Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Balance Type:	na
Period Type:	duration

- Definition

The date the derivative matures.

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount borrowed under the credit facility as of the balance-sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 22
-Article 5

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 129
-Paragraph 2, 4

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 22
-Article 5

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Balance Type:	credit
Period Type:	instant

- Definition

Aggregate notional amount of all interest rate derivatives designated as hedging instruments in fair value hedges. Notional amount refers to the monetary amount specified in the interest rate derivative contract.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt instrument interest.

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Balance Type:	na
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- Definition

Maturity period of term loan.

+ Details

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Namespace Prefix:	wsh
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Balance Type:	na
Period Type:	instant

- Definition

Term loan.

+ Details

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Namespace Prefix:	wsh
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant