| **Accumulated other comprehensive loss (Tables)**                        | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| **Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Accumulated other comprehensive loss                                     | The following table presents the changes in accumulated other comprehensive loss, net of tax: Pensions and OtherPostretirementBenefitsForeign CurrencyTranslationAdjustmentsAccumulated OtherComprehensive LossBalance at December 31, 2010 $(159)  $(261)  $(420) Translation adjustments —  (43)  (43) Amortization of prior service cost (2)  —  (2) Amortization of actuarial net loss 14  —  14 Actuarial net loss arising in the year (148)  —  (148) Deferred taxes 44  —  44 Balance at December 31, 2011 (251)  (304)  (555) Translation adjustments —  78  78 Amortization of prior service cost (2)  —  (2) Amortization of actuarial net loss 22  —  22 Actuarial net loss arising in the year (66)  —  (66) Plan amendments 60  —  60 Deferred taxes (13)  —  (13) Balance at December 31, 2012 $(250)  $(226)  $(476)  |

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| - Definition
Tabular disclosure of the components of accumulated other comprehensive income (loss).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=20435746&loc=SL7669686-108580
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