Financial Instruments and Derivatives - Credit Risk (Details) - Credit risk	Dec. 31, 2017	Dec. 31, 2016
Investment grade
Disclosure of credit risk exposure [line items]
Concentration percentage	95.00%
More than 90 days \| Trade receivables
Disclosure of credit risk exposure [line items]
Concentration percentage	4.00%	3.00%

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

No definition available.

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