Financing Arrangement (Narrative) (Details) (USD $)				1 Months Ended		1 Months Ended				42 Months Ended			1 Months Ended	9 Months Ended
	Dec. 31, 2012	Mar. 31, 2012		Jul. 31, 2011 Convertible Note Hedge	Jul. 14, 2011 Convertible Note Hedge	Jul. 31, 2011 Warrants	Dec. 31, 2012 Warrants	Jul. 14, 2011 Warrants	Jul. 14, 2011 0.75% Convertible Senior Notes Due 2016	Feb. 29, 2016 Revolving Credit Facility [Member]	Sep. 30, 2012 Revolving Credit Facility [Member]	Aug. 30, 2012 Revolving Credit Facility [Member]	Jul. 31, 2011 0.75% Convertible Senior Notes Due 2016 days	Dec. 31, 2012 0.75% Convertible Senior Notes Due 2016	Jul. 14, 2011 0.75% Convertible Senior Notes Due 2016	Jul. 14, 2011 0.75% Convertible Senior Notes Due 2016 Liability Component	Jul. 14, 2011 0.75% Convertible Senior Notes Due 2016 Equity Component
Financing Arrangements
Principal amount	$ 632,500,000	$ 632,500,000							$ 632,500,000
Contractual interest rate of 0.75% Convertible Senior Notes due 2016	0.75%	0.75%												0.75%	0.75%
Convertible Senior Notes due description													2016	2016
0.75% Convertible Senior Notes due 2016 maturity date													Jul. 15, 2016
Conversion rate of Notes													31.5075
Face amount of Notes															1,000
Initial conversion price per share of Notes															$ 31.74
Number of trading days greater than or equal to the initial conversion price													20
Consecutive trading days under conversion trigger													30
Trigger price as percent of conversion price													130.00%
Trigger price													$ 41.26
Number of trading day that trading price falls below 98% of last reported sales price multiplied by conversion rate													5
Consecutive trading days under conversion trigger, trading price													10
Debt trading price as a percentage of stock price times conversion rate													98.00%
Convertible Senior Notes, Carrying Value	554,000,000	539,000,000	[1]													525,000,000
Effective interest rate															4.54%
Debt issuance costs											2,000,000				15,000,000	13,000,000	2,000,000
Debt instrument remaining discount amortization period														3 years 6 months
Shares covered by Hedge Transactions					19,900,000
Strike price for convertible note hedge					$ 31.74
Amount paid for Convertible Note Hedge				107,000,000
Shares covered by warrants issuance								19,900,000
Strike price of warrants							41.14	41.14
Proceeds from Warrants transaction						65,000,000
Line of Credit Facility
Line of Credit Facility, Maximum Borrowing Capacity												500,000,000
Line of Credit Facility Term										3 years 6 months
Option To Request Additional Commitments On Credit Facility												$ 250,000,000

[1] Derived from audited consolidated financial statements.