Debt (Details 1) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Long-term debt:
Commercial paper	$ 604,343	$ 415,936
Global revolving credit facility	26,542	1,000
Unsecured U.S. notes - Medium-term notes	2,635,151	2,484,712
Unsecured U.S. obligations, principally bank term loans	105,500	105,000
Unsecured foreign obligations	303,374	300,516
Capital lease obligations	45,235	48,047
Total before fair market value adjustment	3,720,145	3,355,211
Fair market value adjustment on notes subject to hedging	19,891	21,843
Total after fair market value adjustment	3,740,036	3,377,054
Current portion of long-term debt, including capital leases	(375,949)	(269,275)
Long-term debt	3,364,087	3,107,779
Total debt	3,745,648	3,382,145
U.S Commercial Paper, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	0.46%	0.40%
Maturity date range, end	2016
Commercial paper	571,897	415,936
Canadian Commerial Paper [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	1.15%	0.00%
Maturity date range, end	2016
Commercial paper	$ 32,446	$ 0
Global Revolving Credit Facility Member
Long-term debt:
Long-term debt, Weighted Average Interest Rate	1.53%	1.52%
Maturity date range, end	2016
Unsecured U.S. notes - Medium-term notes, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	4.23%	4.49%
Maturity date range, start	2012
Maturity date range, end	2025
Unsecured U.S. obligations, principally bank term loans, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	1.70%	1.78%
Maturity date range, start	2012
Maturity date range, end	2017
Unsecured Foreign Obligations, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	2.31%	2.71%
Maturity date range, start	2014
Maturity date range, end	2016
Capital Lease Obligations, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	4.12%	4.24%
Maturity date range, start	2012
Maturity date range, end	2018