| **Long term debt (Details) - USD ($) $ in Millions**                | 12 Months Ended |
|---------------------------------------------------------------------|-----------------|
||
| **Debt Instrument [Line Items]**                                    |            |   |   |
| Proceeds from Issuance of Long-term Debt                            | $ 670           | $ 600 | $ 360 |
| Long-term Debt, Current Maturities                                  | 170             | 80 |   |
| Repayments of Long-term Debt                                        | 130             | 260 | $ 0 |
| Pollution Control Revenue Bonds at 2,125%                           | 98              |   |   |
| Pollution Control Revenue Bonds at 2.375%                           | 21              |   |   |
| Pollution Control Revenue Bonds, rates at 2.13% and 2.38%, due 2033 | $ 119           | $ 119 |   |

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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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Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt classified as current. Excludes lease obligation.
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Represents the current and noncurrent portions of a debt security issued by a state, certain agencies or authorities, a local government, or development corporation to finance the construction of air- or water-pollution control facilities or sewage or solid waste disposal facilities pursuant to federal law. The bonds are backed by the credit of the beneficiary of the financing rather than the credit of the issuer.
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The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.
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The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.
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