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v3.19.3.a.u2

Significant Events - Other Disclosures (Details) $ / shares in Units, $ in Millions, $ in Millions |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Oct. 19, 2018 MW | Aug. 02, 2018 CAD ($) | Jul. 20, 2018 CAD ($) | Jun. 28, 2018 CAD ($) | Jun. 22, 2018 CAD ($) $ / shares shares | May 31, 2018 CAD ($) MW | Mar. 15, 2018 CAD ($) | Mar. 15, 2018 USD ($) | Nov. 01, 2017 USD ($) | Oct. 12, 2017 CAD ($) | Oct. 02, 2017 CAD ($) | Aug. 01, 2017 USD ($) | Mar. 01, 2017 CAD ($) | Nov. 18, 2016 CAD ($) | Dec. 31, 2018 CAD ($) MW | Jun. 30, 2018 MW | Dec. 31, 2019 CAD ($) | Dec. 31, 2018 CAD ($) MW | Dec. 31, 2018 USD ($) | Dec. 31, 2017 CAD ($) MW | Dec. 31, 2016 CAD ($) | Dec. 31, 2018 USD ($) MW | Mar. 17, 2016 shares
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Transfer of equity from non-controlling interests |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |  |  |  |
Issued preferred capital |  |  |  | $ 33 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares issued | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,824,620
Net proceeds on sale of non-controlling interest in subsidiary (Note 4) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | $ 144 |  | $ 0 |  |  |
Bonds issued |  |  | $ 345 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings, interest rate basis |  |  | 4.509 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Alberta Off-Coal Agreement |  |  | $ 40 |  |  |  |  |  |  |  |  |  |  |  |  |  | 40 | 40 |  | $ 40 |  |  |
Alberta off-coal agreement, annual cash payments, net |  |  | $ 37 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,267 |  | 3,212 | 3,267 |  |  |  |  |
Notional amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,234 |  | 3,104 | 3,234 |  |  |  |  |
Reversal of unused provision |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 | $ 5 |  |  |  |  |
Force Majeure Relief Claim |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reversal of unused provision |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 94 |  |  |  |  |  |  |  |  |
Kent Hills 3 Wind Project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in contractual power capacity (in megawatts) | MW | 167 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lakeswind |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  | 12 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lakeswind | Property, plant and equipment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  | 11 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lakeswind | Intangible assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  | $ 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Wintering Hills | Wind and Solar |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease through classified as held for sale, investment property |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 28 |  |
Proceeds from sale of assets held for sale |  |  |  |  |  |  |  |  |  |  |  |  | $ 61 |  |  |  |  |  |  |  |  |  |
Windrise |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 207 |  |  | 207 |  |  |  | 207 |
Renewable electricity support agreement, term |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 years |  |  |  |  |  |  |  |
Windrise | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for development project expenditure |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 270 |  |  |  |  |
Windrise | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for development project expenditure |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 285 |  |  |  |  |
TransAlta Renewables |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares issued | shares |  |  |  |  | 11,860,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Par value per share | $ / shares |  |  |  |  | $ 12.65 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from changes in ownership interests in subsidiaries that do not result in loss of control |  |  |  |  | $ 150 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds on sale of non-controlling interest in subsidiary (Note 4) |  |  |  |  | $ 144 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares outstanding | shares |  |  |  |  | 161,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity participation percentage |  |  |  |  | 61.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
TransAlta Renewables | Three Renewable Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid (received) |  |  |  |  |  | $ 166 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value of equity consideration received |  |  |  |  |  | 62 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Portion of consideration paid (received) consisting of cash and cash equivalents |  |  |  |  |  | $ 104 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
TransAlta Renewables | Kent Breeze |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  | 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
TransAlta Renewables | Lakeswind Solar Projects |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  | 21 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
TransAlta Renewables | Lakeswind Wind Farm |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
New Brunswick Power Corporation | Kent Hills 3 Wind Project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of facility (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 17.25 |  |  |
Solomon Power Station | Fortescue Metals Group Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consideration paid (received) |  |  |  |  |  |  |  |  |  |  |  | $ (335) |  |  |  |  |  |  |  |  |  |  |
Portion of consideration paid (received) consisting of cash and cash equivalents |  |  |  |  |  |  |  |  | $ (325) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Kent Hills Wind L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.55% |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 17.00% |  |  |  |  |  |
Kent Hills Wind L.P. | Kent Hills 3 Wind Project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in contractual power capacity (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 17.25 |  |  |  |  |  |  |
Kent Hills Wind L.P. | Kent Hills 3 Wind Project | Natural Forces Technologies Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proportion of ownership interests held by non-controlling interests |  |  |  |  |  |  |  |  |  |  | 17.00% |  |  |  |  |  |  |  |  |  |  |  |
Debentures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  | 6.40% | 6.40% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Borrowings |  | $ 400 |  |  |  |  |  |  |  |  |  |  |  |  | $ 647 |  | $ 647 | 647 |  |  |  |  |
Redemption of noncurrent borrowings |  | 425 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption of prepayment premium recognized in net interest expense |  | 19 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 651 |  | 651 | $ 651 |  |  |  |  |
Accrued and unpaid interest |  | $ 6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debentures | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.00% |  |  | 5.00% |  |  |  | 5.00% |
Debentures | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.30% |  |  | 7.30% |  |  |  | 7.30% |
Debentures | Canadian Hydro Developers Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption of noncurrent borrowings |  |  |  |  |  |  |  |  |  | $ 201 |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption of prepayment premium recognized in net interest expense |  |  |  |  |  |  |  |  |  | 6 |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption of unsecured debt, principal |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 191 |  |  |  |  |  |
Accrued and unpaid interest |  |  |  |  |  |  |  |  |  | $ 4 |  |  |  |  |  |  |  |  |  |  |  |  |
6.65% Senior notes, due May 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  | 6.65% |  |  |  |  |  |  | 6.65% |  |  | 6.65% |  |  |  | 6.65% |
Borrowings |  |  |  |  |  |  |  | $ 500 |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500 |
Redemption of noncurrent borrowings |  |  |  |  |  |  | $ 617 | $ 516 |  |  |  |  |  |  |  |  |  | $ 617 | $ 516 |  |  |  |
Redemption of prepayment premium recognized in net interest expense |  |  |  |  |  |  | $ 5 |  |  |  |  |  |  |  |  |  |  | 5 |  |  |  |  |
Accrued and unpaid interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14 |  |  |  |  |
Bond, 4.454%, November 2033 maturity | Kent Hills Wind L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  |  |  |  |  |  |  |  | 4.454% |  |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  |  |  |  |  | $ 260 |  |  |  |  |  |  |  |  |  |  |  |

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