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Decommissioning and Other Provisions | 12 Months Ended
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Dec. 31, 2017
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract] |
Decommissioning and Other Provisions | Decommissioning and Other Provisions The change in decommissioning and other provision balances is as follows:
| Decommissioning and restoration |  | Other |  | Total |
Balance, Dec. 31, 2015 | 233 |  | 165 |  | 398 |
Liabilities incurred | 11 |  | 12 |  | 23 |
Liabilities settled | (23 | ) | (36 | ) | (59 | )
Accretion | 19 |  | 1 |  | 20 |
Revisions in estimated cash flows | 12 |  | 5 |  | 17 |
Revisions in discount rates | 44 |  | — |  | 44 |
Reversals | — |  | (96 | ) | (96 | )
Change in foreign exchange rates | (3 | ) | (1 | ) | (4 | )
Balance, Dec. 31, 2016 | 293 |  | 50 |  | 343 |
Liabilities incurred | 3 |  | 19 |  | 22 |
Liabilities settled | (19 | ) | (31 | ) | (50 | )
Liabilities disposed(1) | (8 | ) | — |  | (8 | )
Accretion | 23 |  | — |  | 23 |
Revisions in estimated cash flows(2) | 41 |  | 1 |  | 42 |
Revisions in discount rates(2) | 110 |  | — |  | 110 |
Reversals | — |  | (4 | ) | (4 | )
Change in foreign exchange rates | (6 | ) | (2 | ) | (8 | )
Balance, Dec. 31, 2017 | 437 |  | 33 |  | 470 |
(1) Relates to the disposition of the Solomon power station and the sale of the Wintering Hills wind facility. (2) During 2017, mainly as a result of the OCA (see Note 4(H)), the discount rates used for the Canadian coal and mining operations decommissioning provisions were changed to the use of 5 to 15-year rates. The use of lower, shorter-term discount rates increased the corresponding liabilities. On average, these rates decreased by approximately 1.60 to 2.10 per cent. Additionally, the amount and timing of cash outflows for certain Canadian coal plants and mining operations was also revised, resulting in an increase to the corresponding liabilities.
| Decommissioning and restoration |  | Other |  | Total |
Balance, Dec. 31, 2016 | 293 |  | 50 |  | 343 |
Current portion | 27 |  | 12 |  | 39 |
Non-current portion | 266 |  | 38 |  | 304 |
Balance, Dec. 31, 2017 | 437 |  | 33 |  | 470 |
Current portion | 40 |  | 27 |  | 67 |
Non-current portion | 397 |  | 6 |  | 403 |
A. Decommissioning and Restoration A provision has been recognized for all generating facilities and mines for which TransAlta is legally, or constructively, required to remove the facilities at the end of their useful lives and restore the sites to their original condition. TransAlta estimates that the undiscounted amount of cash flow required to settle these obligations is approximately $1 billion, which will be incurred between 2018 and 2073. The majority of the costs will be incurred between 2020 and 2050. At Dec. 31, 2017, the Corporation had provided a surety bond in the amount of US$139 million (2016 - US$139 million) in support of future decommissioning obligations at the Centralia coal mine. At Dec. 31, 2017, the Corporation had provided letters of credit in the amount of $120 million (2016 - $117 million) in support of future decommissioning obligations at the Alberta mine. Some of the facilities that are co-located with mining operations do not currently have any decommissioning obligations recorded as the obligations associated with the facilities are indeterminate at this time. B. Other Provisions Other provisions include amounts related to a portion of the Corporation’s fixed price commitments under several natural gas transportation contracts for firm transportation that is not expected to be used and for vacant leased premises. Accordingly, the unavoidable costs of meeting these obligations exceed the economic benefits expected to be received. The contracts extend to 2023. Other provisions also include provisions arising from ongoing business activities and include amounts related to commercial disputes between the Corporation and customers or suppliers. Information about the expected timing of settlement and uncertainties that could impact the amount or timing of settlement has not been provided as this may impact the Corporation’s ability to settle the provisions in the most favourable manner. During 2015, the Corporation recorded a significant adjustment to other provisions, relating to the force majeure claim at Keephills 1. However, on Nov. 18, 2016, force majeure relief was granted to the Corporation and accordingly approximately $94 million was reversed during the last quarter of 2016 as disclosed in Note 4(I).

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