Debt (Details) (USD $)	6 Months Ended
Jun. 30, 2011
Debt (Textuals) [Abstract]
Additional borrowing capacity	$ 990,000,000
Absorption of reduction to shareholders' equity to remain in compliance with covenant	533,000,000
Financial covenants	2
Borrowings under Five Year Revolving Credit Agreement	0
Principal amount of Zero Coupon Convertible Senior Notes	108,000,000
Accreted value principal amount of Zero Coupon Convertible Senior Notes	58,000,000
Term of repurchase of senior notes	On July 20, 2011 and every five years thereafter
Zero Coupon Convertible Senior Notes due 2031 [Member]
Short-term Debt [Line Items]
Repurchase of senior notes for cash	$ 0

Absorption of reduction to shareholders' equity to remain in compliance with covenant.

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- Definition

Accreted value principal amount of Zero Coupon Convertible Senior Notes.

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- Definition

Debt instrument repurchase term.

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- Definition

Debt Textuals.

+ Details

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- Definition

Financial covenants.

+ Details

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- Definition

Line Of Credit Facility Increase Additional Borrowing.

+ Details

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ 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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- Definition

The cash outflow for a debt where holder has highest claim on the entity's asset in case of bankruptcy or liquidation during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 18

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 20
-Subparagraph b

+ Details

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- Definition

Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

+ 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

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- 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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