Debt (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Lines of Credit [Abstract]
Available and unused lines of credit	$ 3,265,700,000	$ 3,258,300,000
Short-Term Borrowings [Abstract]
Short-term borrowings	11,700,000	9,500,000
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	2,500,500,000	2,501,300,000
Long-term notes payable, unamortized discount on Senior Notes	(7,300,000)	(7,600,000)
Long-term notes payable, deferred gain from termination of interest rate swaps on Senior Notes due 2016	28,600,000	30,500,000
Long-term notes payable, total	2,521,800,000	2,524,200,000
Long-term notes payable, current portion	400,000	700,000
Long-Term Notes Payable	2,521,400,000	2,523,500,000
Convertible Debt [Abstract]
Convertible debt, total	659,400,000	659,400,000
Convertible debt, current	0	0
Convertible Debt	659,400,000	659,400,000
Credit Agreement expiring October 2016 [Member]
Lines of Credit [Abstract]
Credit Agreement, maximum borrowing capacity	2,500,000,000
Credit Agreement, expiration date	October 12, 2016
Available and unused lines of credit	2,500,000,000	2,500,000,000
Credit Agreement expiring October 2016 [Member] | Commercial Paper [Member]
Lines of Credit [Abstract]
Credit Agreement, maximum borrowing capacity	1,500,000,000
Uncommitted lines of credit [Member]
Lines of Credit [Abstract]
Available and unused lines of credit	765,700,000	758,300,000
5.90% Senior Notes due April 15, 2016 [Member]
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	1,000,000,000	1,000,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	5.90%
Maturity date	Apr. 15, 2016
6.25% Senior Notes due July 15, 2019 [Member]
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	500,000,000	500,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	6.25%
Maturity date	Jul. 15, 2019
4.45% Senior Notes due August 15, 2020 [Member]
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	1,000,000,000	1,000,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	4.45%
Maturity date	Aug. 15, 2020
Other notes and loans [Member]
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	500,000	1,300,000
Convertible Notes - due July 31, 2032 [Member]
Convertible Debt [Abstract]
Convertible debt, total	252,700,000	252,700,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	0.00%
Maturity date	Jul. 31, 2032
Convertible Notes - due June 15, 2033 [Member]
Convertible Debt [Abstract]
Convertible debt, total	100,000	100,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	0.00%
Maturity date	Jun. 15, 2033
Convertible Notes - due July 1, 2038 [Member]
Convertible Debt [Abstract]
Convertible debt, total	$ 406,600,000	$ 406,600,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	0.00%
Maturity date	Jul. 01, 2038