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Common Shares (Tables) | 12 Months Ended
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Dec. 31, 2021
Share Capital, Reserves And Other Equity Interest [Abstract] |
Issued and outstanding | TransAlta is authorized to issue an unlimited number of voting common shares without nominal or par value.
As at Dec. 31 | 2021 | 2020
| Common shares (millions) | Amount | Common shares (millions) | Amount
Issued and outstanding, beginning of year | 269.8 |  | 2,896 |  | 277.0 |  | 2,978 |
Purchased and cancelled under the NCIB | — |  | — |  | (7.3) |  | (79) |
Effects of share-based payment plans | — |  | (3) |  | — |  | (3) |
Stock options exercised | 1.2 |  | 8 |  | 0.1 |  | — |
Issued and outstanding, end of year | 271.0 |  | 2,901 |  | 269.8 |  | 2,896 |
The following are the effects of the Company's purchase and cancellation of the common shares during the year:
For the year ended Dec. 31 | 2021 | 2020
Total shares purchased(1) | — |  | 7,352,600 |
Average purchase price per share | — |  | $8.33 |
Total cost | — |  | 61 |
Weighted average book value of shares cancelled | — |  | 79 |
Amount recorded in deficit | — |  | 18 |
(1) As at Dec. 31, 2021, includes nil (2020 — 456,200) shares that were repurchased but were not cancelled due to timing differences between the transaction date and settlement date. 2021 On May 25, 2021, the Toronto Stock Exchange ("TSX") accepted the notice filed by the Company to implement an NCIB for a portion of our common shares. Pursuant to the NCIB, TransAlta may repurchase up to a maximum of 14,000,000 common shares, representing approximately 7.16 per cent of its public float of common shares as at May 18, 2021. Purchases under the NCIB may be made through open market transactions on the TSX and any alternative Canadian trading platforms on which the common shares are traded, based on the prevailing market price. Any common shares purchased under the NCIB will be cancelled. The period during which TransAlta is authorized to make purchases under the NCIB commenced on May 31, 2021 and ends on May 30, 2022, or such earlier date on which the maximum number of common shares are purchased under the NCIB or the NCIB is terminated at the Company’s election. No common shares have been repurchased under the current and previous NCIB in 2021. 2020 On May 26, 2020, the Company announced that the TSX accepted the notice filed by the Company to implement an NCIB for a portion of its common shares. Pursuant to the NCIB, the Company was permitted to purchase up to a maximum of 14,000,000 common shares, representing approximately 7.02 per cent of its issued and common shares as at May 25, 2020. All preferred shares issued and outstanding are non-voting cumulative redeemable fixed or floating rate first preferred shares.
As at Dec. 31 | 2021 | 2020
Series | Number of shares (millions) | Amount | Number of shares (millions) | Amount
Series A | 9.6 |  | 235 |  | 10.2 |  | 248 |
Series B | 2.4 |  | 58 |  | 1.8 |  | 45 |
Series C | 11.0 |  | 269 |  | 11.0 |  | 269 |
Series E | 9.0 |  | 219 |  | 9.0 |  | 219 |
Series G | 6.6 |  | 161 |  | 6.6 |  | 161 |
Issued and outstanding, end of year | 38.6 |  | 942 |  | 38.6 |  | 942 |
Earnings per share |
Year ended Dec. 31 | 2021 | 2020 | 2019
Net earnings (loss) attributable to common shareholders | (576) |  | (336) |  | 52 |
Basic and diluted weighted average number of common shares outstanding (millions) | 271 |  | 275 |  | 283 |
Net earnings (loss) per share attributable to common shareholders, basic and diluted | (2.13) |  | (1.22) |  | 0.18 |

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