| **Summary of significant accounting policies (Product Warranty Liability) (Details) (USD $)In Millions, except Per Share data, unless otherwise specified**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 3 Months Ended | 6 Months Ended |        |
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| **Accrued Product Warranty And Deferred Warranty Revenue, Standard And Extended Warranty Programs, Roll Forward:**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |           |                |   |  |   |   |   |   |
| Accrued product warranty and deferred warranty revenue, at beginning of period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |           |                | $ 598  |  |   | $ 598 | $ 506 |   |
| Cost accrued and revenues deferred                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |           |                |   |  |   | 236 | 175 |   |
| Adjustments to pre-existing warranties                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |           |                |   |  |   | 227 | 36 |   |
| Payments and revenues recognized                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |           |                |   |  |   | (217) | (187) |   |
| Accrued product warranty and deferred warranty revenue, at end of period                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 844            |                |   |  | 530 | 844 | 530 |   |
| Less: Current portion                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 365            |                |   |  | 240 | 365 | 240 |   |
| Noncurrent accrued product warranty and deferred warranty revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 479            |                |   |  | 290 | 479 | 290 |   |
| Adjustment for Changes in Estimate to Preexisting Warranty                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 104            | [1]            | 123    | [1] |   |   | 27 |   |
| Product Warranty Accrual, Preexisting Increase (Decrease), net of tax                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 100            |                | 119    |  |   | 24 |   |   |
| Product Warranty Accrual, Preexisting Increase Decrease Per Share, Net of Tax                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       | $ 1.46         |                | $ 1.7  |  |   | $ 0.31 |   |   |
| **Extended Warranty Program:**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |           |                |   |  |   |   |   |   |
| Extended warranty program deferred revenue                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          | 308            |                |   |  |   | 308 |   | 257 |
| Revenue recognized under extended warranty programs                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 16             |                |   |  | 13 | 31 | 25 |   |
| Revenue extended warranty service contracts                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |           |                |   |  |   | $ 24 |   |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| [1]Adjustments to pre-existing warranties reflect changes in our estimate of warranty costs for products sold in prior periods. Such adjustments typically occur when claims experience deviates from historic and expected trends. Our warranty liability is generally affected by component failure rates, repair costs, and the timing of failures. Future events and circumstances related to these factors could materially change our estimates and require adjustments to our liability. In addition, new product launches require a greater use of judgment in developing estimates until historical experience becomes available. In the first quarter of 2012, we recorded adjustments for changes in estimates of $123 million, $119 million net of tax, or $1.70 per diluted share. In the second quarter of 2012, we recorded adjustments for changes in estimates of $104 million, $100 million net of tax, or $1.46 per diluted share. In the second quarter of 2011, we recorded adjustments for changes in estimates of $27 million, $24 million net of tax, or $0.31 per diluted share. |

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Carrying value as of the balance sheet date of obligations incurred through that date and payable for estimated claims under standard and extended warranty protection rights granted to customers.
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Carrying value as of the balance sheet date of obligations incurred through that date and payable for estimated claims under standard and extended warranty protection rights granted to customers. For classified balance sheets, represents the current portion of the liabilities (due within one year or within the normal operating cycle if longer).
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Carrying value as of the balance sheet date of obligations incurred through that date and due after one year (or beyond the operating cycle if longer) for estimated claims under standard and extended warranty protection rights granted to customers.
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Represents the aggregate decrease in the liability related to payments to satisfy claims for standard and extended product warranties.
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Represents the aggregate Increase or Decrease in the liability during the reporting period for accruals related to preexisting standard and extended product warranties (including adjustments for changes in estimates).
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Represents the aggregate increase in the liability for accruals related to standard and extended product warranties issued during the reporting period.
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