Financing Arrangements (Details) (USD $)			1 Months Ended	3 Months Ended	1 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2011 3.375% Senior Notes due September 15, 2021	Mar. 31, 2013 3.375% Senior Notes due September 15, 2021	Feb. 29, 2004 1.5% Convertible Senior Notes due February 15, 2024	Mar. 31, 2013 1.5% Convertible Senior Notes due February 15, 2024
Financing Arrangements
Issue price of notes			$ 500,000,000		$ 330,000,000
Proceeds from notes			492,000,000		323,000,000
Redemption option, price as a percentage of principal				100.00%
Percentage of principal amount plus accrued and unpaid interest at which holders have right to sell notes to company				101.00%
Debt instrument interest rate (as a percent)	5.625%		3.375%	3.375%	1.50%	1.50%
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01			$ 0.01
Notes convertible into common shares, conversion rate per $1,000 principal amount of Notes (in shares)					36.2815
Conversion rate of 36.2815 shares per $1,000 principal amount of Notes					$ 1,000