Fair value (Details 8)	Dec. 31, 2015
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Number of investment managers of plan assets	15
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Number of investment managers of plan assets	1

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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