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Timing of revenue recognition (Details) - KRW (₩)
₩ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of performance obligations [Line Items]      
Total revenue from external customers ₩ 57,925,837 ₩ 58,568,082 ₩ 60,033,062
Domestic      
Disclosure of performance obligations [Line Items]      
Total revenue from external customers 56,774,578 56,942,128 57,799,991
Domestic | Performance obligations satisfied at point in time      
Disclosure of performance obligations [Line Items]      
Total revenue from external customers 56,380,608 56,609,330 57,514,866
Domestic | Performance obligations satisfied over time      
Disclosure of performance obligations [Line Items]      
Total revenue from external customers 393,970 332,798 285,125
Overseas      
Disclosure of performance obligations [Line Items]      
Total revenue from external customers [1] 1,151,259 1,625,954 2,233,071
Overseas | Performance obligations satisfied at point in time      
Disclosure of performance obligations [Line Items]      
Total revenue from external customers 303,704 285,546 382,938
Overseas | Performance obligations satisfied over time      
Disclosure of performance obligations [Line Items]      
Total revenue from external customers ₩ 847,555 ₩ 1,340,408 ₩ 1,850,133
[1] Middle East and other Asian countries make up the majority of overseas revenue and non-current assets. Since the overseas revenue or non-current assets attributable to particular countries are not material, they are not disclosed individually.