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Segments Disclosures - Reported Segment Earnings (Loss) and Segment Assets (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Disclosure of operating segments [line items] |  |  |
Revenues | $ 2,721 | $ 2,101 | $ 2,347
Fuel and purchased power | 1,054 | 805 | 881
Carbon compliance | 178 | 163 | 205
Gross margin | 1,489 | 1,133 | 1,261
OM&A | 511 | 472 |
Taxes, other than income taxes | 32 | 33 | 29
Net other operating expense (income) | 8 | (11) | (49)
Termination of Sundance B and C PPAs | 0 | 0 | (56)
Adjusted EBITDA |  |  |
Equity income from associate | 9 | 1 | 0
Finance lease income | 25 | 7 | 6
Depreciation and amortization | (529) | (654) | (590)
Asset impairment | (648) | (84) | (25)
Gains on disposals of investments | 0 | 0 | 88
Net interest expense | 245 | 238 | 179
Foreign exchange gain (loss) | 16 | 17 | (15)
Gains on disposals of non-current assets | 54 | 9 | 46
Earnings (loss) before income taxes | (380) | (303) | 193
Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 2,721 | 2,101 | 2,347
Fuel and purchased power | 1,054 | 805 | 881
OM&A | 511 |  | 475
Net other operating expense (income) | 8 | (11) |
Operating segments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 2,768 | 2,174 | 2,344
Fuel and purchased power | 843 | 618 | 756
Carbon compliance | 178 | 163 | 205
Gross margin | 1,747 | 1,393 | 1,383
OM&A | 491 | 472 |
Taxes, other than income taxes | 33 | 33 | 29
Net other operating expense (income) | (40) | (39) | (49)
Termination of Sundance B and C PPAs |  |  | (56)
Adjusted EBITDA | 1,263 | 927 | 984
Operating segments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 2,739 | 2,104 | 2,347
Fuel and purchased power | 1,054 | 805 | 881
OM&A | 513 |  | 475
Net other operating expense (income) | 8 | (11) |
Operating segments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (34) | 42 | (33)
Operating segments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 41 | 17 | 24
Operating segments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 25 | 7 | 6
Operating segments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (3) | 4 |
Operating segments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | (4) | (4) | (4)
Operating segments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | (190) | (146) | (121)
Operating segments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | (17) | (37) |
Operating segments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | (28) |  |
Operating segments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 6 |  |
Operating segments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | (48) |  |
Operating segments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | (28) |
Material reconciling items |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (29) | (70) | 3
Fuel and purchased power | 211 | 187 | 125
Carbon compliance | 0 | 0 | 0
Gross margin | (240) | (257) | (122)
OM&A | 22 | 0 |
Taxes, other than income taxes | 0 | 0 | 0
Net other operating expense (income) | 48 | 28 | 0
Termination of Sundance B and C PPAs |  |  | 0
Adjusted EBITDA |  |  |
Material reconciling items | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Fuel and purchased power | 0 | 0 | 0
OM&A | 0 |  | 0
Net other operating expense (income) | 0 | 0 |
Material reconciling items | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 34 | (42) | 33
Material reconciling items | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (41) | (17) | (24)
Material reconciling items | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (25) | (7) | (6)
Material reconciling items | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 3 | (4) |
Material reconciling items | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 4 | 4 | 4
Material reconciling items | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 190 | 146 | 121
Material reconciling items | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 17 | 37 |
Material reconciling items | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 28 |  |
Material reconciling items | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | (6) |  |
Material reconciling items | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | 48 |  |
Material reconciling items | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | 28 |
Material reconciling items | Contribution from equity accounted investments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (18) | (3) |
Fuel and purchased power | 0 | 0 |
Carbon compliance | 0 | 0 |
Gross margin | (18) | (3) |
OM&A | (2) | 0 |
Taxes, other than income taxes | (1) | 0 |
Net other operating expense (income) | 0 | 0 |
Adjusted EBITDA |  |  |
Material reconciling items | Contribution from equity accounted investments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (18) | (3) |
Fuel and purchased power | 0 | 0 |
OM&A | (2) |  |
Net other operating expense (income) | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Material reconciling items | Contribution from equity accounted investments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Material reconciling items | Contribution from equity accounted investments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Material reconciling items | Contribution from equity accounted investments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | 0 |  |
Material reconciling items | Contribution from equity accounted investments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | 0 |
Hydro | Operating segments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 383 | 152 | 156
Fuel and purchased power | 16 | 8 | 7
Carbon compliance | 0 | 0 | 0
Gross margin | 367 | 144 | 149
OM&A | 42 | 37 |
Taxes, other than income taxes | 3 | 2 | 3
Net other operating expense (income) | 0 |  | 0
Termination of Sundance B and C PPAs |  |  | 0
Adjusted EBITDA | 322 | 105 | 110
Hydro | Operating segments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 383 | 152 | 156
Fuel and purchased power | 16 | 8 | 7
OM&A | 42 |  | 36
Net other operating expense (income) | 0 | 0 |
Hydro | Operating segments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Hydro | Operating segments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Hydro | Operating segments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Hydro | Operating segments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Hydro | Operating segments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Hydro | Operating segments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Hydro | Operating segments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Hydro | Operating segments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Hydro | Operating segments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Hydro | Operating segments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | 0 |  |
Hydro | Operating segments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | 0 |
Wind and Solar | Operating segments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 348 | 334 | 295
Fuel and purchased power | 17 | 25 | 16
Carbon compliance | 0 | 0 | 0
Gross margin | 331 | 309 | 279
OM&A | 59 | 53 |
Taxes, other than income taxes | 10 | 8 | 8
Net other operating expense (income) | 0 |  | (10)
Termination of Sundance B and C PPAs |  |  | 0
Adjusted EBITDA | 262 | 248 | 231
Wind and Solar | Operating segments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 323 | 332 | 312
Fuel and purchased power | 17 | 25 | 16
OM&A | 59 |  | 50
Net other operating expense (income) | 0 | 0 |
Wind and Solar | Operating segments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 25 | 2 | (17)
Wind and Solar | Operating segments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Wind and Solar | Operating segments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Wind and Solar | Operating segments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Wind and Solar | Operating segments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Wind and Solar | Operating segments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Wind and Solar | Operating segments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Wind and Solar | Operating segments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Wind and Solar | Operating segments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Wind and Solar | Operating segments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | 0 |  |
Wind and Solar | Operating segments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | 0 |
Gas | Operating segments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 1,132 | 848 | 887
Fuel and purchased power | 374 | 221 | 230
Carbon compliance | 118 | 120 | 138
Gross margin | 640 | 507 | 519
OM&A | 173 | 166 |
Taxes, other than income taxes | 13 | 13 | 9
Net other operating expense (income) | (40) | (39) | (41)
Termination of Sundance B and C PPAs |  |  | (14)
Adjusted EBITDA | 494 | 367 | 403
Gas | Operating segments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 1,109 | 787 | 851
Fuel and purchased power | 457 | 325 | 315
OM&A | 175 |  | 162
Net other operating expense (income) | (40) | (11) |
Gas | Operating segments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (40) | 33 | 6
Gas | Operating segments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 41 | 17 | 24
Gas | Operating segments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 25 | 7 | 6
Gas | Operating segments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (3) | 4 |
Gas | Operating segments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | (4) | (4) | (4)
Gas | Operating segments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | (79) | (100) | (81)
Gas | Operating segments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Gas | Operating segments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | (2) |  |
Gas | Operating segments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Gas | Operating segments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | 0 |  |
Gas | Operating segments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | (28) |
Energy Transition |  |  |
Disclosure of operating segments [line items] |  |  |
Asset impairment | (191) |  |
Energy Transition | Operating segments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 728 | 690 | 893
Fuel and purchased power | 432 | 352 | 499
Carbon compliance | 60 | 48 | 77
Gross margin | 236 | 290 | 317
OM&A | 97 | 106 |
Taxes, other than income taxes | 6 | 9 | 8
Net other operating expense (income) | 0 | 0 | 0
Termination of Sundance B and C PPAs |  |  | (42)
Adjusted EBITDA | 133 | 175 | 227
Energy Transition | Operating segments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 709 | 704 | 905
Fuel and purchased power | 560 | 435 | 539
OM&A | 117 |  | 124
Net other operating expense (income) | 48 | 0 |
Energy Transition | Operating segments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 19 | (14) | (12)
Energy Transition | Operating segments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Transition | Operating segments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Transition | Operating segments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Energy Transition | Operating segments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Energy Transition | Operating segments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | (111) | (46) | (40)
Energy Transition | Operating segments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | (17) | (37) |
Energy Transition | Operating segments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | (26) |  |
Energy Transition | Operating segments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 6 |  |
Energy Transition | Operating segments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | (48) |  |
Energy Transition | Operating segments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | 0 |
Energy Marketing | Operating segments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 173 | 143 | 119
Fuel and purchased power | 0 | 0 | 0
Carbon compliance | 0 | 0 | 0
Gross margin | 173 | 143 | 119
OM&A | 36 | 30 |
Taxes, other than income taxes | 0 | 0 | 0
Net other operating expense (income) | 0 | 0 | 0
Termination of Sundance B and C PPAs |  |  | 0
Adjusted EBITDA | 137 | 113 | 89
Energy Marketing | Operating segments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 211 | 122 | 129
Fuel and purchased power | 0 | 0 | 0
OM&A | 36 |  | 30
Net other operating expense (income) | 0 | 0 |
Energy Marketing | Operating segments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | (38) | 21 | (10)
Energy Marketing | Operating segments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Marketing | Operating segments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Marketing | Operating segments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Energy Marketing | Operating segments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Energy Marketing | Operating segments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Energy Marketing | Operating segments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Energy Marketing | Operating segments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Energy Marketing | Operating segments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Energy Marketing | Operating segments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | 0 |  |
Energy Marketing | Operating segments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | 0 |
Corporate | Operating segments |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 4 | 7 | (6)
Fuel and purchased power | 4 | 12 | 4
Carbon compliance | 0 | (5) | (10)
Gross margin | 0 | 0 | 0
OM&A | 84 | 80 |
Taxes, other than income taxes | 1 | 1 | 1
Net other operating expense (income) | 0 | 0 | 2
Termination of Sundance B and C PPAs |  |  | 0
Adjusted EBITDA | (85) | (81) | (76)
Corporate | Operating segments | Previously Reported |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 4 | 7 | (6)
Fuel and purchased power | 4 | 12 | 4
OM&A | 84 |  | 73
Net other operating expense (income) | 0 | 0 |
Corporate | Operating segments | Unrealized mark-to-market (gain) loss |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate | Operating segments | Decrease in finance lease receivable |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate | Operating segments | Finance lease income |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate | Operating segments | Unrealized foreign exchange gain on commodity |  |  |
Disclosure of operating segments [line items] |  |  |
Revenues | 0 | 0 |
Corporate | Operating segments | Australian interest income |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | 0
Corporate | Operating segments | Mine depreciation |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 | $ 0
Corporate | Operating segments | Coal inventory write-down |  |  |
Disclosure of operating segments [line items] |  |  |
Fuel and purchased power | 0 | 0 |
Corporate | Operating segments | Parts and materials write-down |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Corporate | Operating segments | Curtailment gain |  |  |
Disclosure of operating segments [line items] |  |  |
OM&A | 0 |  |
Corporate | Operating segments | Royalty onerous contract and contract termination penalties |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) | $ 0 |  |
Corporate | Operating segments | Impact of Sheerness going off-coal |  |  |
Disclosure of operating segments [line items] |  |  |
Net other operating expense (income) |  | $ 0 |

X
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Namespace Prefix: | ifrs-full_
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