Debt (Details Textual) (USD $)	6 Months Ended
Jun. 30, 2012
Line of Credit Facility [Line Items]
Borrowings against credit facility	$ 980,000,000
Long-Term Debt (Textual) [Abstract]
Funds available under revolving credit facility	85,000,000
Outstanding letters of credit under various bilateral committed letter of credit facilities	2,054,000,000
Interest rate under multicurrency facility	LIBOR, NIBOR or EURIBOR plus 0.22%
Variable rate basis	LIBOR, NIBOR or EURIBOR
Variable rate	0.22%
Five year revolving credit facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	2,000,000,000
Borrowings against credit facility	$ 935,000,000
5.65% interest payable semi annually on Senior Notes due on November 15, 2012 [Member]
Debt (Textual) [Abstract]
Senior notes interest rate	5.65%
5.5% interest payable semi annually on Senior Notes due on November 19, 2012 [Member]
Debt (Textual) [Abstract]
Senior notes interest rate	5.50%
6.125% interest payable semi annually on Senior Notes due on August 15, 2015 [Member]
Debt (Textual) [Abstract]
Senior notes interest rate	6.125%

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Interest rate under multicurrency facility.

+ References

No definition available.

+ Details

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- Details

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- Definition

Outstanding letters of credit under various bilateral committed letter of credit facilities.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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- 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- 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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- Details

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- 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

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: 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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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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