Debt (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Long-term debt:
Unsecured U.S. notes - Medium-term notes	$ 2,971,313	$ 2,484,712
Unsecured U.S. obligations, principally bank term loans	105,500	105,000
Unsecured foreign obligations	313,406	300,516
Capital lease obligations	42,018	48,047
Total before fair market value adjustment	3,794,251	3,355,211
Fair market value adjustment on notes subject to hedging	16,725	21,843
Total after fair market value adjustment	3,810,976	3,377,054
Current portion of long-term debt, including capital leases	(358,155)	(269,275)
Long-term debt	3,452,821	3,107,779
Total debt	3,820,796	3,382,145
U.S Commercial Paper, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	0.41%	0.40%
Commercial Paper	329,925	415,936
Maturity date range, start	Jan. 01, 2016
Canadian Commerial Paper [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	1.14%	0.00%
Commercial Paper	23,165	0
Maturity date range, start	Jan. 01, 2016
Global Revolving Credit Facility [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	1.58%	1.52%
Maturity date range, start	Jan. 01, 2016
Long-term Line of Credit, Noncurrent	$ 8,924	$ 1,000
Unsecured U.S. notes - Medium-term notes, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	4.01%	4.49%
Maturity date range, start	Jan. 01, 2013
Maturity date range, end	Dec. 31, 2025
Unsecured U.S. obligations, principally bank term loans, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	1.56%	1.78%
Maturity date range, start	Jan. 01, 2013
Maturity date range, end	Dec. 31, 2017
Unsecured Foreign Obligations, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	1.91%	2.71%
Maturity date range, start	Jan. 01, 2013
Maturity date range, end	Dec. 31, 2016
Capital Lease Obligations, Long-Term [Member]
Long-term debt:
Long-term debt, Weighted Average Interest Rate	4.08%	4.24%
Maturity date range, start	Jan. 01, 2013
Maturity date range, end	Dec. 31, 2018