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Sensitivity analysis for electricity rates (Details) - KRW (₩)
₩ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Increase (decrease) of income before income tax    
Disclosure of Sensitivity analysis for electricity rates [Line Items]    
1% Increase ₩ 559,390 ₩ 568,420
1% Decrease (559,390) (568,420)
Increase (decrease) of shareholder's equity    
Disclosure of Sensitivity analysis for electricity rates [Line Items]    
1% Increase [1] 559,390 568,420
1% Decrease [1] ₩ (559,390) ₩ (568,420)
[1] The effect on the shareholders' equity excluding the impact of income taxes.