Debt (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Lines of Credit [Abstract]
Available and unused lines of credit	$ 3,546,100,000	$ 3,551,500,000
Short-Term Borrowings [Abstract]
Short-term borrowings	7,500,000	5,900,000
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	3,750,500,000	3,750,500,000
Unamortized premium (discount) on Senior Notes, net	14,400,000	14,700,000
Deferred gain from termination of interest rate swaps on Senior Notes due 2016	14,100,000	15,900,000
Long-term notes payable, total	3,779,000,000	3,781,100,000
Long-term notes payable, current portion	400,000	400,000
Long-Term Notes Payable	3,778,600,000	3,780,700,000
Convertible Debt [Abstract]
Convertible debt, current	252,700,000	0
Convertible Debt	0	252,700,000
Credit Agreement expiring October 2016 [Member]
Lines of Credit [Abstract]
Credit Agreement, expiration date	Oct. 12, 2016
Available and unused lines of credit	2,500,000,000	2,500,000,000
Credit Agreement, covenant terms	The Credit Agreement contains financial covenants that require us to maintain a Leverage Ratio of consolidated indebtedness to consolidated EBITDA to no more than 3 times for the most recently ended 12-month period (under the Credit Agreement, EBITDA is defined as earnings before interest, taxes, depreciation and amortization) and an Interest Coverage Ratio of consolidated EBITDA to interest expense of at least 5 times for the most recently ended 12-month period.
Credit Agreement, covenant compliance	At March 31, 2014 we were in compliance with these covenants, as our Leverage Ratio was 1.9 times and our Interest Coverage Ratio was 10.8 times.
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	1,046,100,000	1,051,500,000
5.90% Senior Notes due April 15, 2016
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
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
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
3.625% Senior Notes due May 1, 2022
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	1,250,000,000	1,250,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	3.625%
Maturity date	May 01, 2022
Other notes and loans
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	500,000	500,000
Convertible Notes - due July 31, 2032
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 debt, put terms	Holders of the Convertible Notes due July 31, 2032 (the “2032 Notes”) have the right to put the notes back to us for cash on July 31 of each year and we have the right to redeem the notes for cash at any time on or after July 31, 2014. There are no events that accelerate the noteholders’ put rights.
Convertible debt, conversion rate	18.373