Financing Arrangements (Details) (USD $)	1 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended						0 Months Ended			0 Months Ended
	Sep. 30, 2011 3.375% Senior Notes due September 15, 2021	Sep. 30, 2014 3.375% Senior Notes due September 15, 2021	Sep. 30, 2014 3.375% Senior Notes due September 15, 2021 Change of control triggering event	Feb. 29, 2004 1.5% Convertible Senior Notes due February 15, 2024	Sep. 30, 2014 1.5% Convertible Senior Notes due February 15, 2024	Sep. 30, 2013 1.5% Convertible Senior Notes due February 15, 2024	Sep. 30, 2014 1.5% Convertible Senior Notes due February 15, 2024 Maximum	Sep. 30, 2013 1.5% Convertible Senior Notes due February 15, 2024 Maximum	Sep. 30, 2014 Credit facilities instrument	Sep. 30, 2014 Credit facilities May 2014 Revolving Loan and Letter of Credit Facility Agreement	Sep. 30, 2014 Credit facilities May 2014 Revolving Loan and Letter of Credit Facility Agreement Maximum	Sep. 30, 2014 Credit facilities May 2014 Revolving Loan and Letter of Credit Facility Agreement Maximum Subsidiaries	Sep. 30, 2014 Credit facilities November 2012 Revolving Loan and Letter of Credit Facility Agreement, as amended	Sep. 30, 2014 Credit facilities November 2012 Revolving Loan and Letter of Credit Facility Agreement, as amended Maximum	Sep. 30, 2014 Credit facilities November 2012 Revolving Loan and Letter of Credit Facility Agreement, as amended Maximum Subsidiaries	Sep. 30, 2014 Credit facilities Revolving advances
Financing Arrangements
Number of credit facilities									2
Maximum borrowing capacity									$ 3,500,000,000	$ 1,700,000,000			$ 1,800,000,000			$ 1,750,000,000
Maximum borrowing capacity additional amount, subject to certain conditions										500,000,000			500,000,000
Ratio of consolidated debt to tangible net worth											100.00%			100.00%
Aggregate amount of debt												750,000,000			750,000,000
Issue price of notes	500,000,000			330,000,000
Debt instrument interest rate (as a percent)	3.375%	3.375%		1.50%	1.50%
Proceeds from notes	492,000,000			323,000,000
Redemption price as a percentage of principal		100.00%	101.00%
Debt conversion, amount of original debt							$ 100,000	$ 100,000
Debt conversions (in shares)					1,750	1,562