| **Income taxes**                            | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
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| **Income Tax Expense (Benefit) [Abstract]** | Â                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Income taxes                                | Income taxesWe compute on a quarterly basis an estimated annual effective tax rate considering ordinary income and related income tax expense. Canadian results in 2011 and 2010 are excluded from ordinary income due to ordinary losses for which no benefit can be recognized. Ordinary income refers to income (loss) before income tax expense excluding significant, unusual, or infrequently occurring items. The tax effect of an unusual or infrequently occurring item is recorded in the interim period in which it occurs. Our 2010 annual effective tax rate included a refund for alternative minimum taxes paid in prior years resulting from the “Worker, Homeownership, and Business Assistance Act of 2009.” Items included in income tax expense in the periods in which they occur include the cumulative effect of changes in tax laws or rates, foreign exchange gains and losses, adjustments to uncertain tax positions, and adjustments to our valuation allowance due to changes in judgment regarding the realizability of deferred tax assets in future years.We have evaluated the need to maintain a valuation allowance for deferred tax assets based on an assessment of whether it is more likely than not that deferred tax benefits will be realized through the generation of future taxable income. Appropriate consideration is given to all available evidence, both positive and negative, in assessing the need for a valuation allowance. Due to the cyclical nature of our U.S and Canadian businesses, the historical inconsistency of profits during the full business cycle, and the softness of the economic outlook, we continue to maintain a full valuation allowance against our U.S and Canadian deferred tax assets. However, it is reasonably possible within the next twelve months that the Company may release all or a portion of its U.S. valuation allowance if U.S. operations continue to improve.We recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such a position are measured based on the largest benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement. As of April 30, 2011, the amount of liability for unrecognized tax benefits was $107 million, net of offsetting indirect tax benefits. If the unrecognized tax benefits are recognized, the entire amount would impact our effective tax rate. However, to the extent we continue to maintain a full valuation allowance against certain deferred tax assets, the effect may be in the form of an increase in the deferred tax asset related to our net operating loss carry forward which would be offset by a full valuation allowance.We recognize interest and penalties related to uncertain tax positions as part of Income tax expense. Total interest and penalties related to our uncertain tax positions are immaterial.We have open tax years back to 2001 with various significant tax jurisdictions in the U.S., Canada, Mexico, and Brazil. In connection with the examination of tax returns, contingencies may arise that generally result from differing interpretations of applicable tax laws and regulations as they relate to the amount, timing or inclusion of revenues or expenses in taxable income, or the sustainability of tax credits to reduce income taxes payable. We believe we have sufficient accruals for our contingent tax liabilities. Interim tax provisions include amounts considered sufficient to pay assessments that may result from examinations of prior year tax returns, although actual results may differ. While the liability for unrecognized tax benefits may increase or decrease during the next twelve months, we do not expect any such change would have a material effect on our financial condition, results of operations, or cash flows. |

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| - Definition
Description containing the entire income tax disclosure. Examples include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information. This element may be used as a single block of text to encapsulate the entire disclosure including data and tables.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 136, 172Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 43, 44, 45, 46, 47, 48, 49
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| - Details**Name:**us-gaap_IncomeTaxExpenseBenefitAbstract**Namespace Prefix:**us-gaap**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |