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Operating Segments - Summary of Breakdown of Revenue by Activity (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of revenue [line Items]      
Revenue from supply of energy R$ 24,872 R$ 23,701 R$ 23,430
Revenue from Use of Distribution Systems (the TUSD charge) 2,045 1,611 1,705
CVA and Other financial components in tariff adjustment 1,973 988 (1,455)
Transmission concession revenue 411 371 312
Transmission construction revenue 96 25 54
Concession assets - indemnity revenue 250 373 751
Generation assets - indemnity revenue 55 271  
Distribution construction revenue 802 1,094 1,139
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified   9 8
Gain on inflation updating of concession grant fee 321 317 300
Transactions in energy on the CCEE 217 860 161
Supply of gas 1,995 1,759 1,444
Fine for violation of continuity indicator (44)    
Other operating revenues 1,585 1,484 1,421
Sector / Regulatory charges reported as Deductions from revenue (12,312) (11,151) (10,497)
Net operating revenue 22,266 21,712 18,773
Eliminations [member]      
Disclosure of revenue [line Items]      
Revenue from supply of energy (78) (81) (67)
Revenue from Use of Distribution Systems (the TUSD charge) (22) (32) (35)
Transmission concession revenue (178) (148) (98)
Other operating revenues (15) (26) (33)
Net operating revenue (293) (288) (234)
Energy Generation [member] | Operating Segments [member]      
Disclosure of revenue [line Items]      
Revenue from supply of energy 7,065 7,340 6,809
Generation assets - indemnity revenue 55 271  
Gain on inflation updating of concession grant fee 321 317 300
Transactions in energy on the CCEE 217 860 161
Other operating revenues 82 37 22
Sector / Regulatory charges reported as Deductions from revenue (1,366) (1,430) (1,322)
Net operating revenue 6,374 7,190 5,875
Transmission [member] | Operating Segments [member]      
Disclosure of revenue [line Items]      
Transmission concession revenue 589 519 410
Transmission construction revenue 96 25 54
Concession assets - indemnity revenue 250 373 751
Other operating revenues 29 9 14
Sector / Regulatory charges reported as Deductions from revenue (288) (167) (211)
Net operating revenue 675 777 1,113
Distribution [member] | Operating Segments [member]      
Disclosure of revenue [line Items]      
Revenue from supply of energy 17,885 16,442 16,688
Revenue from Use of Distribution Systems (the TUSD charge) 2,067 1,643 1,740
CVA and Other financial components in tariff adjustment 1,973 988 (1,455)
Distribution construction revenue 757 1,045 1,102
Adjustment to expectation of cash flow from Financial assets of distribution concession to be indemnified   9 8
Fine for violation of continuity indicator (44)    
Other operating revenues 1,345 1,175 1,134
Sector / Regulatory charges reported as Deductions from revenue (10,226) (9,177) (8,620)
Net operating revenue 13,757 12,312 10,597
Gas [member] | Operating Segments [member]      
Disclosure of revenue [line Items]      
Distribution construction revenue 45 49 37
Supply of gas 1,995 1,759 1,444
Other operating revenues   1  
Sector / Regulatory charges reported as Deductions from revenue (421) (327) (301)
Net operating revenue 1,619 1,482 1,181
Telecoms [member] | Operating Segments [member]      
Disclosure of revenue [line Items]      
Other operating revenues   168 159
Sector / Regulatory charges reported as Deductions from revenue   (41) (34)
Net operating revenue   127 125
Other [member] | Operating Segments [member]      
Disclosure of revenue [line Items]      
Other operating revenues 144 120 125
Sector / Regulatory charges reported as Deductions from revenue (11) (9) (9)
Net operating revenue R$ 134 R$ 112 R$ 116