OTHER ASSETS AND OTHER LIABILITIES - The fair value of derivative financial instruments (Details)
S/ in Thousands, $ in Millions
 12 Months Ended
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2019
PEN (S/)
Dec. 31, 2018
PEN (S/)
Jan. 01, 2018
PEN (S/)
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     S/ 1,092,107 S/ 766,317 S/ 701,826
Liabilities     1,040,282 715,804  
Nominal amount     69,720,506 56,935,229  
Derivatives held for trading [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     992,936 622,132  
Liabilities     970,671 654,909  
Nominal amount     63,449,868 49,995,816  
Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     99,171 144,185  
Liabilities     69,611 60,895  
Nominal amount     6,270,638 6,939,413  
Forward foreign exchange contracts one [Member] | Derivatives held for trading [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     306,148 124,124  
Liabilities     246,960 101,548  
Nominal amount     27,422,634 17,557,683  
Maturity January 2020 / October 2022 January 2019 / September 2020      
Related instruments -        
Interest Rate Swap          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     268,633 141,731  
Liabilities     350,938 148,119  
Interest Rate Swap | Derivatives held for trading [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     268,633 141,731  
Liabilities     350,938 148,119  
Nominal amount     26,268,071 21,890,962  
Maturity January 2020 / December 2031 January 2019 / December 2031      
Related instruments -        
Cross Currency Swap          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     411,656 354,432  
Liabilities     366,545 401,856  
Cross Currency Swap | Derivatives held for trading [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     411,656 354,432  
Liabilities     366,545 401,856  
Nominal amount     8,177,179 9,999,343  
Maturity January 2020 / January 2033 January 2019 / January 2033      
Related instruments -        
Foreign exchange options [Member] | Derivatives held for trading [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     6,489 1,281  
Liabilities     6,089 728  
Nominal amount     1,565,083 306,321  
Maturity January 2020 / December 2020 January 2019 / November 2020      
Related instruments -        
Futures [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     10 564  
Liabilities     139 2,658  
Futures [Member] | Derivatives held for trading [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     10 564  
Liabilities     139 2,658  
Nominal amount     16,901 241,507  
Maturity March 2020 March 2019      
Interest rate swap contract one [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     102 4,364  
Liabilities     1,111 123  
Nominal amount     662,800 1,180,550  
Maturity May 2020 / November 2020 January 2019 / August 2019      
Related instruments Debt to banks        
Interest rate swap contract one [Member] | Fair value hedges [member] | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 11,694  
Liabilities     8,124 4,867  
Nominal amount     618,790 923,912  
Maturity June 2021 / May 2023 July 2019 / July 2025      
Related instruments Investments (*)        
Interest rate swap contract two [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 3,445  
Liabilities     1,046 67  
Nominal amount     629,660 843,250  
Maturity May 2020 / June 2020 February 2019 / November 2019      
Related instruments Debt to banks        
Interest rate swap contract three [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     55 312  
Liabilities     714 0  
Nominal amount     984,258 337,300  
Maturity February 2020 / November 2020 May 2019      
Related instruments Debt to banks        
Interest rate swap contract four [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     315 209  
Liabilities     839 233  
Nominal amount     994,200 505,950  
Maturity May 2020 / August 2020 May 2019 / October 2019      
Related instruments Debt to banks        
Interest rate swap contract five [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     114 0  
Liabilities     0 0  
Nominal amount     331,400 0  
Maturity August 2020 -      
Related instruments Debt to banks        
Interest rate swap contract six [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     447 0  
Nominal amount     331,400 0  
Maturity June 2020 -      
Related instruments Debt to banks        
Interest rate swap contract seven [Member] | Cash flow hedges          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Nominal amount   $ 150.0   506,000  
Interest rate swap contract seven [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     0 151  
Nominal amount     0 337,300  
Maturity - July 2019      
Related instruments Debt to banks        
Interest rate swap contract eight [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 3,417  
Liabilities     0 0  
Nominal amount     0 505,950  
Maturity - March 2019 / December 2019      
Related instruments Repurchase agreements        
Interest rate swap contract nine [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     2,555 0  
Nominal amount     231,980 0  
Maturity March 2021 -      
Cross currency swap contract [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     30,741 35,229  
Liabilities     0 0  
Nominal amount     231,980 236,110  
Maturity August 2020 August 2020      
Related instruments Repurchase agreements        
Cross currency swap contract one [Member] | Cash flow hedges          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Nominal amount $ 70.0 $ 70.0 232,000 236,100  
Cross currency swap contract one [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     30,352 11,939  
Nominal amount     149,130 151,785  
Maturity August 2026 August 2026      
Related instruments Repurchase agreements        
Cross currency swap contract two [Member] | Cash flow hedges          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Nominal amount $ 45.0 $ 45.0 149,100 151,800  
Cross currency swap contract two [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     12,236 1,741  
Nominal amount     82,850 84,325  
Maturity August 2026 August 2026      
Related instruments Repurchase agreements        
Cross currency swap contract three [Member] | Cash flow hedges          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Nominal amount $ 25.0 $ 25.0 82,900 84,300  
Cross currency swap contract three [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     20,803 21,424  
Liabilities     1,167 1,867  
Nominal amount     107,425 136,119  
Maturity May 2021 / September 2024 February 2021 / September 2024      
Related instruments Investments (*)        
Cross currency swap contract four [Member] | Cash flow hedges          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Nominal amount     107,400 136,100  
Cross currency swap contract four [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     0 4,249  
Nominal amount     0 77,822  
Maturity - March 2019      
Related instruments Investments (*)        
Cross currency swap contract five [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     7,624 16,132  
Liabilities     0 0  
Nominal amount     331,400 337,300  
Maturity January 2020 January 2020      
Related instruments Debt to banks        
Cross currency swap contract five [Member] | Fair value hedges [member] | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Nominal amount     618,800 923,900  
Cross currency swap contract six [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     0 35,658  
Nominal amount     0 1,011,900  
Maturity - October 2019      
Related instruments Bonds issued        
Cross currency swap contract seven [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     8,197 0  
Nominal amount     165,700 0  
Maturity January 2025 -      
Related instruments Bonds issued        
Cross currency swap contract eight [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     0 0  
Liabilities     2,823 0  
Nominal amount     152,545 0  
Maturity August 2021 -      
Related instruments Bonds issued        
Cross currency swap and interest rate swap contract [Member] | Cash flow hedges          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Nominal amount $ 80.0 $ 80.0 265,100 269,800  
Cross currency swap and interest rate swap contract [Member] | Cash flow hedges | Derivatives held as hedges [Member]          
Disclosure of Other Assets And Other Liabilities [Line Items]          
Assets     39,417 47,959  
Liabilities     0 0  
Nominal amount     S/ 265,120 S/ 269,840  
Maturity August 2020 August 2020      
Related instruments Repurchase agreements