Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Debt - Commercial Paper (Details) - USD ($)			6 Months Ended
Debt - Commercial Paper (Details) - USD ($)	Jul. 31, 2015	Feb. 28, 2014	Jun. 30, 2018	Dec. 31, 2017	Mar. 26, 2015
Commercial Paper \| United States
Line of Credit Facility [Line Items]
Maturity period of debt		397 days	26 days 4 hours 19 minutes 12 seconds
Maximum borrowing capacity under credit facility					$ 1,800,000,000
Weighted average interest rate on debt			2.36%
Commercial Paper \| Europe
Line of Credit Facility [Line Items]
Maturity period of debt	183 days		26 days 12 hours 43 minutes 12 seconds
Weighted average interest rate on debt			(0.20%)
Carrying value \| United States
Line of Credit Facility [Line Items]
Commercial paper			$ 508,460,000	$ 228,500,000
Carrying value \| Europe
Line of Credit Facility [Line Items]
Commercial paper			$ 560,748,000	$ 912,146,000