Debt (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended				0 Months Ended		12 Months Ended							12 Months Ended					12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			1 Months Ended	12 Months Ended			95 Months Ended	1 Months Ended	12 Months Ended			82 Months Ended		1 Months Ended		12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2004	Aug. 18, 2011 Interest Rate Swaps on 2016 Notes [Member]	Dec. 31, 2010 Interest Rate Swaps on 2016 Notes [Member]	Dec. 31, 2011 Commercial paper and Credit Agreement [Member]	Dec. 31, 2010 Commercial paper and Credit Agreement [Member]	Dec. 31, 2009 Commercial paper and Credit Agreement [Member]	Dec. 31, 2011 Credit Agreement expiring October 2016 [Member]	Dec. 31, 2010 Credit Agreement expiring December 2013 [Member]	Dec. 31, 2011 Uncommitted lines of credit [Member]	Dec. 31, 2010 Uncommitted lines of credit [Member]	Dec. 31, 2011 Long-Term Notes Payable [Member]	Dec. 31, 2010 Long-Term Notes Payable [Member]	Dec. 31, 2009 Long-Term Notes Payable [Member]	Dec. 31, 2011 5.90% Senior Notes due April 15, 2016 [Member]	Dec. 31, 2010 5.90% Senior Notes due April 15, 2016 [Member]	Dec. 31, 2011 6.25% Senior Notes due July 15, 2019 [Member]	Dec. 31, 2010 6.25% Senior Notes due July 15, 2019 [Member]	Dec. 31, 2011 4.45% Senior Notes due August 15, 2020 [Member]	Dec. 31, 2010 4.45% Senior Notes due August 15, 2020 [Member]	Dec. 31, 2011 Other notes and loans at rates from 2.8% to 9.0%, due through 2013 [Member]	Dec. 31, 2010 Other notes and loans at rates from 2.8% to 9.0%, due through 2013 [Member]	Dec. 31, 2011 Convertible Debt [Member]	Dec. 31, 2010 Convertible Debt [Member]	Dec. 31, 2009 Convertible Debt [Member]	Feb. 28, 2001 Convertible Notes - due February 7, 2031 [Member]	Dec. 31, 2011 Convertible Notes - due February 7, 2031 [Member]	Dec. 31, 2010 Convertible Notes - due February 7, 2031 [Member]	Dec. 31, 2009 Convertible Notes - due February 7, 2031 [Member]	Dec. 31, 2008 Convertible Notes - due February 7, 2031 [Member]	Mar. 31, 2002 Convertible Notes - due July 31, 2032 [Member]	Dec. 31, 2011 Convertible Notes - due July 31, 2032 [Member]	Dec. 31, 2010 Convertible Notes - due July 31, 2032 [Member]	Dec. 31, 2009 Convertible Notes - due July 31, 2032 [Member]	Dec. 31, 2008 Convertible Notes - due July 31, 2032 [Member]	Dec. 31, 2004 Convertible Notes - due July 31, 2032 [Member] Y	Jun. 30, 2006 Convertible Notes - due June 15, 2033 [Member]	Jun. 30, 2003 Convertible Notes - due June 15, 2033 [Member]	Dec. 31, 2011 Convertible Notes - due June 15, 2033 [Member]	Dec. 31, 2010 Convertible Notes - due June 15, 2033 [Member]	Jun. 30, 2010 Convertible Notes - due July 1, 2038 [Member]	Dec. 31, 2011 Convertible Notes - due July 1, 2038 [Member]	Dec. 31, 2010 Convertible Notes - due July 1, 2038 [Member]	Dec. 31, 2009 Convertible Notes - due July 1, 2038 [Member]	Dec. 31, 2004 Convertible Notes - due July 1, 2038 [Member] Y	Dec. 31, 2011 Commercial Paper [Member] Credit Agreement expiring October 2016 [Member]
Lines of Credit [Abstract]
Credit Agreement, initiation date										October 2011
Credit Agreement, maximum borrowing capacity										$ 2,500,000,000	$ 2,000,000,000																																					$ 1,500,000,000
Credit Agreement, expiration date										October 12, 2016
Available and unused lines of credit	3,258,300,000	2,610,400,000								2,500,000,000	2,000,000,000	758,300,000	610,400,000
Credit Agreement, covenant terms										The Credit Agreement contains financial covenants that limit the ratio of total consolidated indebtedness to total consolidated EBITDA (under the Credit Agreement, EBITDA is defined as earnings before interest, taxes, depreciation and amortization) to no more than 3.0 times. We are also required to maintain a minimum ratio of consolidated EBITDA to interest expense of at least 5.0 times.
Credit Agreement, covenant compliance										At December 31, 2011 we were in compliance with these covenants, as our ratio of debt to EBITDA was 1.7 times and our ratio of EBITDA to interest expense was 12.3 times.
Short-Term Borrowings [Abstract]
Short-term borrowings	9,500,000	50,200,000
Short-term borrowings, weighted average interest rate	5.60%	5.40%
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	2,501,300,000	2,501,500,000															1,000,000,000	1,000,000,000	500,000,000	500,000,000	1,000,000,000	1,000,000,000	1,300,000	1,500,000
Long-term notes payable, unamortized discount on Senior Notes	(7,600,000)	(8,700,000)
Long-term notes payable, deferred gain from termination of interest rate swaps on Senior Notes due 2016	30,500,000	0			33,200,000
Long-term notes payable, fair value hedge adjustment on Senior Notes due 2016	0	(26,300,000)
Long-term notes payable, total	2,524,200,000	2,466,500,000
Long-term notes payable, current portion	700,000	1,400,000
Long-Term Notes Payable	2,523,500,000	2,465,100,000
Interest rate swaps, amount of hedged item						1,000,000,000
Interest rate swaps, proceeds from termination of interest rate swaps	38,800,000	0	0		38,800,000
Interest rate swaps, fair value						24,200,000
Convertible Debt [Abstract]
Convertible debt, total	659,400,000	659,500,000																											0	100,000				252,700,000	252,700,000						100,000	100,000		406,600,000	406,600,000
Convertible debt, current	0	0
Convertible Debt	659,400,000	659,500,000
Convertible debt, issuance of debt																												850,000,000					900,000,000							600,000,000
Convertible debt, repayments of convertible debt																														5,700,000	841,200,000	3,000,000				474,300,000	173,000,000		132,500,000				60,800,000		60,800,000
Convertible debt, number of potential common shares																																		4.6							7.9
Convertible debt, conversion price																																		$ 55.01							$ 51.50
Convertible debt, put terms																																		Holders of these notes have the right to put the notes back to us for cash on July 31 of each year. There are no events that accelerate the noteholders’ put rights.										Holders of these notes have the right to put the notes back to us for cash on June 15, 2013, 2018 and 2023 and on each June 15 annually thereafter through June 15, 2037 and we have a right to redeem the notes for cash on June 17, 2013 and June 15, 2018. After June 15, 2018, we can redeem the 2038 Notes at any time. There are no events that accelerate the noteholders’ put rights.
Convertible debt, indenture amendment																																							substantially all of the remaining 2033 Notes were amended to extend the maturity of the notes from June 15, 2033 to July 1, 2038. The amendments conformed other terms of the notes for the extension of the maturity date, as well as amending the comparable yield. The amended notes are referred to as our Zero Coupon Zero Yield Convertible Notes due 2038 (“2038 Notes”).				In June 2010, the indenture governing the 2038 Notes was amended. Holders of $403.2 million of the 2038 Notes agreed to waive their right to contingent cash interest, if payable, from December 15, 2010 through and including December 15, 2013. Holders of $3.4 million of the 2038 Notes did not put their notes to us for repurchase and did not consent to the amendment
Convertible debt, equity component				47,500,000
Convertible debt, equity component, net of tax				28,500,000
Convertible debt, equity component, amortization period																																						1									1.6
Convertible debt, supplemental interest paid	0	25,900,000	35,200,000																											0	27,600,000				5,700,000	7,600,000									20,200,000	0
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate																	5.90%		6.25%		4.45%													0.00%							0.00%			0.00%
Interest rate, minimum																							2.80%
Interest rate, maximum																							9.00%
Maturity date																	Apr. 15, 2016		Jul. 15, 2019		Aug. 15, 2020								Feb. 07, 2031					Jul. 31, 2032							Jun. 15, 2033
Maturity date range, end																							2013
Components of Interest Expense [Abstract]
Interest expense, debt							2,500,000	1,800,000	5,700,000					125,800,000	106,700,000	78,000,000									10,000,000	10,500,000	22,700,000
Interest expense, fees	7,100,000	5,700,000	5,100,000
Interest expense, other	12,700,000	10,000,000	10,700,000
Interest expense, total	158,100,000	134,700,000	122,200,000
Stated Maturities of Long-Term Notes Payable and Convertible Debt [Abstract]
Stated maturities of long-term notes payable and convertible debt, 2012	700,000
Stated maturities of long-term notes payable and convertible debt, 2013	300,000
Stated maturities of long-term notes payable and convertible debt, 2014	300,000
Stated maturities of long-term notes payable and convertible debt, 2015	0
Stated maturities of long-term notes payable and convertible debt, 2016	1,000,000,000
Stated maturities of long-term notes payable and convertible debt, Thereafter	2,159,400,000
Stated maturities of long-term notes payable and convertible debt, Total	$ 3,160,700,000