Debt Schedule of Debt (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Short-term debt and current portion of long-term debt:
Short-term debt, weighted-average interest rate	1.39%	1.07%
Short-term debt	$ 136,016,000	$ 177,629,000
Current portion of long-term debt	452,836,000	613,781,000
Total short-term debt and current portion of long-term debt	588,852,000	791,410,000
Long-term debt:
Total before fair market value adjustment	5,262,553,000	5,226,756,000
Fair market value adjustment on notes subject to hedging	100,000	1,110,000
Total after fair market value adjustment	5,248,828,000	5,213,645,000
Current portion of long-term debt	(452,836,000)	(613,781,000)
Long-term debt	4,795,992,000	4,599,864,000
Total debt	5,384,844,000	5,391,274,000
Unamortized original issue discounts	7,000,000	7,000,000
Aggregate notional amount of interest rate swaps	$ 675,000,000	$ 825,000,000
U.S commercial paper
Long-term debt:
Long-term debt, weighted-average interest rate	1.29%	0.87%
U.S. commercial paper	$ 724,618,000	$ 342,480,000
Global revolving credit facility
Long-term debt:
Long-term debt, weighted-average interest rate	0.00%	2.06%
Global revolving credit facility	$ 0	$ 4,703,000
Unsecured U.S. notes - Medium-term notes
Long-term debt:
Long-term debt, weighted-average interest rate	2.71%	2.67%
Unsecured U.S. notes - Medium-term notes	$ 3,713,858,000	$ 4,113,421,000
Debt issuance costs	$ (13,825,000)	$ (14,221,000)
Unsecured U.S. obligations
Long-term debt:
Long-term debt, weighted-average interest rate	2.45%	2.19%
Unsecured U.S. obligations	$ 50,000,000	$ 50,000,000
Unsecured foreign obligations
Long-term debt:
Long-term debt, weighted-average interest rate	1.50%	1.55%
Obligations	$ 223,707,000	$ 232,092,000
Asset-backed U.S. obligations
Long-term debt:
Long-term debt, weighted-average interest rate	1.85%	1.80%
Obligations	$ 527,476,000	$ 459,876,000
Capital lease obligations
Long-term debt:
Long-term debt, weighted-average interest rate	3.29%	3.17%
Capital lease obligations	$ 22,894,000	$ 24,184,000