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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19)(a)(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13)(2))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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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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Debt - Commercial Paper (Details) - USD ($)			3 Months Ended
Debt - Commercial Paper (Details) - USD ($)	Jul. 31, 2015	Feb. 28, 2014	Mar. 31, 2018	Dec. 31, 2017	Mar. 26, 2015
Commercial Paper \| United States
Line of Credit Facility [Line Items]
Maturity period of debt		397 days	24 years 2 months 1 day
Maximum borrowing capacity under credit facility					$ 1,800,000,000
Weighted average interest rate on debt			2.34%
Commercial Paper \| Europe
Line of Credit Facility [Line Items]
Maturity period of debt	183 days		25 years 6 months 9 days
Weighted average interest rate on debt			(0.20%)
Carrying value \| United States
Line of Credit Facility [Line Items]
Commercial paper			$ 342,400,000	$ 228,500,000
Carrying value \| Europe
Line of Credit Facility [Line Items]
Commercial paper			$ 935,921,000	$ 912,146,000