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Operating segments (Details) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | ₩ 60,033,062 | ₩ 59,335,889 | ₩ 59,763,087
Intersegment revenue | 0 | 0 | 0
Revenue from external customers | 60,033,062 | 59,335,889 | 59,763,087
Depreciation and amortisation | 10,024,794 | 9,773,711 | 8,960,988
Interest income | 223,767 | 206,143 | 241,778
Interest expense | 1,868,458 | 1,789,552 | 1,752,868
Employee benefit expense | 360,575 | 391,360 | 373,753
Loss on abandonment of property, plant and equipment | 481,176 | 424,091 | 426,519
Increase in provisions, net | 1,056,994 | 1,690,120 | 1,782,732
Operating profit (loss) | (685,109) | 5,319,869 | 12,296,360
Finance income | 796,870 | 1,530,618 | 791,543
Finance expense | (2,470,743) | (3,127,952) | (2,437,087)
Profit (loss) related to associates and joint ventures | 358,163 | (108,317) | (137,348)
Profit (loss) before income tax | (2,000,819) | 3,614,218 | 10,513,468
Segment assets | 185,249,061 | 181,788,915 | 177,837,042
Investments in associates and joint ventures | 5,878,345 | 5,330,696 | 5,510,448
Acquisition of non-current assets | 12,377,457 | 12,679,845 | 12,153,211
Segment liabilities | 114,156,299 | 108,824,274 | 104,786,497
Operating segments |  |  |
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | 97,262,180 | 94,974,836 | 95,611,310
Intersegment revenue | 37,229,118 | 35,638,947 | 35,848,223
Revenue from external customers | 60,033,062 | 59,335,889 | 59,763,087
Depreciation and amortisation | 10,081,743 | 9,833,297 | 9,006,486
Interest income | 268,043 | 230,685 | 264,764
Interest expense | 1,912,094 | 1,818,399 | 1,778,479
Employee benefit expense | 391,055 | 421,827 | 400,072
Loss on abandonment of property, plant and equipment | 481,176 | 424,091 | 426,519
Increase in provisions, net | 1,049,005 | 2,076,867 | 1,785,741
Operating profit (loss) | (557,368) | 5,152,814 | 12,543,173
Profit (loss) related to associates and joint ventures | 358,163 | (108,317) | (137,348)
Segment assets | 223,823,428 | 220,561,693 | 216,061,727
Investments in associates and joint ventures | 5,878,345 | 5,330,696 | 5,510,448
Acquisition of non-current assets | 12,440,174 | 12,656,229 | 12,345,112
Segment liabilities | 115,812,546 | 110,538,279 | 107,405,716
Operating segments | Transmission and distribution |  |  |
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | 59,676,952 | 59,486,766 | 59,862,284
Intersegment revenue | 1,393,120 | 2,044,160 | 1,890,489
Revenue from external customers | 58,283,832 | 57,442,606 | 57,971,795
Depreciation and amortisation | 3,555,158 | 3,466,410 | 3,226,700
Interest income | 77,925 | 49,987 | 80,882
Interest expense | 708,329 | 737,971 | 844,200
Employee benefit expense | 144,180 | 158,738 | 162,326
Loss on abandonment of property, plant and equipment | 424,774 | 384,595 | 424,356
Increase in provisions, net | 580,931 | 885,195 | 711,430
Operating profit (loss) | (1,814,363) | 1,902,634 | 5,274,308
Profit (loss) related to associates and joint ventures | 287,268 | (105,166) | (128,402)
Segment assets | 107,486,379 | 106,540,154 | 105,321,129
Investments in associates and joint ventures | 3,671,897 | 3,366,309 | 4,121,462
Acquisition of non-current assets | 6,323,504 | 6,606,512 | 6,345,004
Segment liabilities | 53,404,610 | 50,757,798 | 49,854,420
Operating segments | Electric power generation (Nuclear) |  |  |
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | 8,858,717 | 9,415,752 | 11,168,579
Intersegment revenue | 8,833,787 | 9,359,468 | 11,129,385
Revenue from external customers | 24,930 | 56,284 | 39,194
Depreciation and amortisation | 3,088,019 | 3,267,510 | 3,130,820
Interest income | 30,422 | 21,034 | 33,111
Interest expense | 503,161 | 487,503 | 474,590
Employee benefit expense | 76,467 | 80,809 | 70,582
Loss on abandonment of property, plant and equipment | 38,886 | 0 | 0
Increase in provisions, net | 520,167 | 801,800 | 576,223
Operating profit (loss) | 357,401 | 1,347,794 | 3,770,165
Profit (loss) related to associates and joint ventures | 9,946 | 3,637 | (1,082)
Segment assets | 55,792,704 | 55,011,096 | 52,782,915
Investments in associates and joint ventures | 43,038 | 11,843 | 15,384
Acquisition of non-current assets | 2,187,077 | 2,083,967 | 1,945,610
Segment liabilities | 30,484,104 | 29,252,816 | 27,366,938
Operating segments | Electric power generation (Non-nuclear) |  |  |
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | 25,204,085 | 22,795,816 | 21,394,223
Intersegment revenue | 24,389,816 | 21,885,251 | 20,561,044
Revenue from external customers | 814,269 | 910,565 | 833,179
Depreciation and amortisation | 3,269,023 | 2,954,375 | 2,523,306
Interest income | 29,313 | 18,860 | 24,171
Interest expense | 577,441 | 486,176 | 359,607
Employee benefit expense | 91,140 | 94,075 | 79,846
Loss on abandonment of property, plant and equipment | 17,516 | 39,335 | 2,133
Increase in provisions, net | (227,234) | 171,457 | 276,619
Operating profit (loss) | 482,418 | 1,523,497 | 3,211,684
Profit (loss) related to associates and joint ventures | 58,993 | (6,718) | (8,342)
Segment assets | 49,296,392 | 47,938,084 | 47,427,642
Investments in associates and joint ventures | 2,114,203 | 1,904,224 | 1,320,203
Acquisition of non-current assets | 3,435,222 | 3,250,524 | 3,508,313
Segment liabilities | 27,558,156 | 26,337,295 | 26,205,049
Operating segments | Plant maintenance & engineering service |  |  |
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | 2,526,126 | 2,621,440 | 2,618,388
Intersegment revenue | 2,170,959 | 2,211,716 | 2,190,207
Revenue from external customers | 355,167 | 409,724 | 428,181
Depreciation and amortisation | 114,030 | 109,001 | 98,843
Interest income | 12,505 | 10,801 | 10,672
Interest expense | 4,126 | 2,967 | 2,156
Employee benefit expense | 77,526 | 87,344 | 86,268
Loss on abandonment of property, plant and equipment | 0 | 161 | 0
Increase in provisions, net | 174,785 | 219,382 | 221,301
Operating profit (loss) | 314,755 | 265,593 | 210,680
Profit (loss) related to associates and joint ventures | 1,956 | (70) | 478
Segment assets | 3,431,068 | 3,273,959 | 3,106,909
Investments in associates and joint ventures | 49,207 | 48,320 | 53,399
Acquisition of non-current assets | 111,393 | 145,779 | 180,715
Segment liabilities | 1,200,390 | 1,176,627 | 1,218,047
Operating segments | Others |  |  |
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | 996,300 | 655,062 | 567,836
Intersegment revenue | 441,436 | 138,352 | 77,098
Revenue from external customers | 554,864 | 516,710 | 490,738
Depreciation and amortisation | 55,513 | 36,001 | 26,817
Interest income | 117,878 | 130,003 | 115,928
Interest expense | 119,037 | 103,782 | 97,926
Employee benefit expense | 1,742 | 861 | 1,050
Loss on abandonment of property, plant and equipment | 0 | 0 | 30
Increase in provisions, net | 356 | (967) | 168
Operating profit (loss) | 102,421 | 113,296 | 76,336
Profit (loss) related to associates and joint ventures | 0 | 0 | 0
Segment assets | 7,816,885 | 7,798,400 | 7,423,132
Investments in associates and joint ventures | 0 | 0 | 0
Acquisition of non-current assets | 382,978 | 569,447 | 365,470
Segment liabilities | 3,165,286 | 3,013,743 | 2,761,262
Material reconciling items |  |  |
Disclosure of operating segments [Line Items] |  |  |
Total segment revenue | (37,229,118) | (35,638,947) | (35,848,223)
Intersegment revenue | (37,229,118) | (35,638,947) | (35,848,223)
Depreciation and amortisation | (56,949) | (59,586) | (45,498)
Interest income | (44,276) | (24,542) | (22,986)
Interest expense | (43,636) | (28,847) | (25,611)
Employee benefit expense | (30,480) | (30,467) | (26,319)
Increase in provisions, net | 7,989 | (386,747) | (3,009)
Operating profit (loss) | (127,741) | 167,055 | (246,813)
Segment assets | (38,574,367) | (38,772,778) | (38,224,685)
Investments in associates and joint ventures | 0 | 0 | 0
Acquisition of non-current assets | (62,717) | 23,616 | (191,901)
Segment liabilities | (1,656,247) | (1,714,005) | ₩ (2,619,219)
Elimination of intersegment amounts |  |  |
Disclosure of operating segments [Line Items] |  |  |
Segment assets | (41,026,970) | (39,517,829) |
Investments in associates and joint ventures | 0 | 0 |
Acquisition of non-current assets | (62,717) | 23,616 |
Segment liabilities | (5,055,737) | (5,239,156) |
Equity method adjustment |  |  |
Disclosure of operating segments [Line Items] |  |  |
Segment assets | 964,234 | 754,314 |
Investments in associates and joint ventures | 0 | 0 |
Acquisition of non-current assets | 0 | 0 |
Segment liabilities | 0 | 0 |
Deferred taxes |  |  |
Disclosure of operating segments [Line Items] |  |  |
Segment assets | 2,131 | 2,215 |
Investments in associates and joint ventures | 0 | 0 |
Acquisition of non-current assets | 0 | 0 |
Segment liabilities | (621) | 5,339,450 |
Others |  |  |
Disclosure of operating segments [Line Items] |  |  |
Segment assets | 1,486,238 | (11,478) |
Investments in associates and joint ventures | 0 | 0 |
Acquisition of non-current assets | 0 | 0 |
Segment liabilities | ₩ 3,400,111 | ₩ (1,814,299) |

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