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Hybrid bond (Details) - KRW (₩)
₩ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Hybrid bond [Line Items]    
Amount ₩ 398,910 ₩ 498,660
Korea Western Power [Member] | 1st bond-type hybrid bond [Member]    
Hybrid bond [Line Items]    
Issue date   Oct. 18, 2012
Amount   ₩ 100,000
Korea South-East Power [Member] | 1st bond-type hybrid bond [Member]    
Hybrid bond [Line Items]    
Issue date Dec. 07, 2012 Dec. 07, 2012
Maturity date Dec. 06, 2042 Dec. 06, 2042
Yield (%) 4.38% 4.38%
Amount ₩ 170,000 ₩ 170,000
Korea South-East Power [Member] | 2nd bond-type hybrid bond [Member]    
Hybrid bond [Line Items]    
Issue date Dec. 07, 2012 Dec. 07, 2012
Maturity date Dec. 06, 2042 Dec. 06, 2042
Yield (%) 4.44% 4.44%
Amount ₩ 230,000 ₩ 230,000
Expense of issuance [Member]    
Hybrid bond [Line Items]    
Amount ₩ (1,090) ₩ (1,340)