Debt (Details) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Lines of Credit [Abstract]
Available and unused lines of credit	$ 3,470,900,000	$ 3,470,900,000		$ 3,378,200,000
Short-Term Borrowings [Abstract]
Short-term borrowings	12,800,000	12,800,000		6,400,000
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	3,750,300,000	3,750,300,000		3,750,400,000
Unamortized premium (discount) on Senior Notes, net	15,300,000	15,300,000		16,000,000
Deferred gain from termination of interest rate swaps on Senior Notes due 2016	19,500,000	19,500,000		23,100,000
Long-term notes payable, total	3,785,100,000	3,785,100,000		3,789,500,000
Long-term notes payable, current portion	300,000	300,000		400,000
Long-Term Notes Payable	3,784,800,000	3,784,800,000		3,789,100,000
Long-term notes payable, proceeds from issuance of long-term notes payable		0	746,800,000
Convertible Debt [Abstract]
Convertible debt, total	252,700,000	252,700,000		659,400,000
Convertible debt, current	0	0		0
Convertible Debt	252,700,000	252,700,000		659,400,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Convertible Debt, Call Date	May 16, 2013
Convertible Debt, Percentage of Principal Amount Redeemed	100.00%
Convertible Debt, Conversion Rate	19.4174
Convertible Debt, Latest Conversion Date	Jun. 13, 2013
Convertible Debt, Principle Amount Settled in Cash	406,100,000
Convertible Debt, Shares Issued for Conversion Premium	1,499,792	1,499,792
Convertible Debt, Repurchase Date	Jun. 17, 2013
Convertible Debt, Repurchase Amount	600,000	600,000
Credit Agreement expiring October 2016 [Member]
Lines of Credit [Abstract]
Credit Agreement, maximum borrowing capacity	2,500,000,000	2,500,000,000
Credit Agreement, expiration date		Oct. 12, 2016
Available and unused lines of credit	2,500,000,000	2,500,000,000		2,500,000,000
Credit Agreement, covenant terms		The Credit Agreement contains financial covenants that restrict our ability to incur indebtedness as defined in the agreement. These financial covenants limit the Leverage Ratio of total consolidated indebtedness to total 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). We are also required to maintain a minimum 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 June 30, 2013 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	1,500,000,000
Uncommitted lines of credit [Member]
Lines of Credit [Abstract]
Available and unused lines of credit	970,900,000	970,900,000		878,200,000
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		1,000,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	5.90%	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		500,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	6.25%	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		1,000,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	4.45%	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		1,250,000,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	3.625%	3.625%
Maturity date		May 01, 2022
Other notes and loans
Long-Term Notes Payable [Abstract]
Long-term notes payable, carrying amount	300,000	300,000		400,000
Convertible Notes due July 31, 2032
Convertible Debt [Abstract]
Convertible debt, total	252,700,000	252,700,000		252,700,000
Long-Term Notes Payable and Convertible Debt [Abstract]
Interest rate	0.00%	0.00%
Maturity date		Jul. 31, 2032
Convertible Notes due June 15, 2033
Convertible Debt [Abstract]
Convertible debt, total	0	0		100,000
Convertible Notes due July 1, 2038
Convertible Debt [Abstract]
Convertible debt, total	$ 0	$ 0		$ 406,600,000