Debt - Schedule of Debt (Details) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Short-term debt and current portion of long-term debt:
Short-term debt, weighted-average interest rate	0.94%	2.26%
Short-term debt	$ 122,354,000	$ 35,947,000
Current portion of long-term debt	924,854,000	598,583,000
Total short-term debt and current portion of long-term debt	1,047,208,000	634,530,000
Long-term debt:
Total before fair market value adjustment	5,505,475,000	5,476,656,000
Fair market value adjustment on notes subject to hedging	20,989,000	5,253,000
Total after fair market value adjustment	5,511,660,000	5,466,680,000
Current portion of long-term debt	(924,854,000)	(598,583,000)
Long-term debt	4,586,806,000	4,868,097,000
Total debt	5,634,014,000	5,502,627,000
Unamortized original issue discounts	7,200,000	7,700,000
Aggregate notional amount of interest rate swaps	$ 825,000,000	$ 825,000,000
U.S commercial paper [Member]
Long-term debt:
Long-term debt, weighted-average interest rate	0.71%	0.55%
U.S. commercial paper	$ 599,605,000	$ 547,130,000
Global revolving credit facility [Member]
Long-term debt:
Long-term debt, weighted-average interest rate	2.01%	2.31%
Global revolving credit facility	$ 53,037,000	$ 25,291,000
Unsecured U.S. notes - Medium-term notes [Member]
Long-term debt:
Long-term debt, weighted-average interest rate	2.88%	2.84%
Unsecured U.S. notes - Medium-term notes	$ 4,113,137,000	$ 4,112,519,000
Debt issuance costs	$ (14,804,000)	$ (15,229,000)
Unsecured U.S. obligations [Member]
Long-term debt:
Long-term debt, weighted-average interest rate	1.86%	1.73%
Unsecured U.S. obligations	$ 50,000,000	$ 50,000,000
Unsecured foreign obligations [Member]
Long-term debt:
Long-term debt, weighted-average interest rate	1.93%	1.92%
Obligations	$ 254,448,000	$ 275,661,000
Asset-backed U.S. obligations [Member]
Long-term debt:
Long-term debt, weighted-average interest rate	1.78%	1.81%
Obligations	$ 407,217,000	$ 434,001,000
Capital lease obligations [Member]
Long-term debt:
Long-term debt, weighted-average interest rate	3.22%	3.31%
Capital lease obligations	$ 28,031,000	$ 32,054,000