Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Outstanding Balance	$ 3,278,000	$ 5,581,000
Face amount of eligible notes issued	$ 2,000,000	$ 2,000,000
Short-term Debt [Member]
Short-term Debt [Line Items]
Year-End Stated Rate on Debt	2.05%	1.20%
Fees to maintain the secured financing facility	$ 9,200	$ 8,600
Commercial Paper [Member]
Short-term Debt [Line Items]
Outstanding Balance	$ 1,168,000	$ 2,993,000
Commercial Paper [Member] | Short-term Debt [Member]
Short-term Debt [Line Items]
Year-End Stated Rate on Debt	1.54%	1.13%
Other Short Term Borrowings [Member]
Short-term Debt [Line Items]
Outstanding Balance	$ 2,110,000	$ 2,588,000
Other Short Term Borrowings [Member] | Bank Overdrafts [Member]
Short-term Debt [Line Items]
Outstanding Balance	$ 132,000	$ 369,000
Other Short Term Borrowings [Member] | Short-term Debt [Member]
Short-term Debt [Line Items]
Year-End Stated Rate on Debt	2.34%	1.28%