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Concession Contract Assets - Summary of Changes in Concession Contract Assets (Detail) - BRL (R$)
R$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of assets recognised from costs to obtain or fulfil contracts with customers [line items]      
Effects of IFRS 15 first-time adoption (Notes 15 and 19) R$ 1,714    
Additions (Note 15e) 893 R$ 25 R$ 2,271
Inflation adjustment 88    
Adjustment to expected contract cash flow from the concession 13    
Amounts received (161)    
Transfers to financial assets (27)    
Transfers to intangible assets (750)    
Transfers to PP&E 1    
Provision for impairment (42)    
Ending balance 1,729    
Transmission [member]      
Disclosure of assets recognised from costs to obtain or fulfil contracts with customers [line items]      
Effects of IFRS 15 first-time adoption (Notes 15 and 19) 1,092    
Additions (Note 15e) 96    
Inflation adjustment 88    
Adjustment to expected contract cash flow from the concession 13    
Amounts received (161)    
Transfers to PP&E 1    
Ending balance 1,129    
Distribution [member]      
Disclosure of assets recognised from costs to obtain or fulfil contracts with customers [line items]      
Effects of IFRS 15 first-time adoption (Notes 15 and 19) 532    
Additions (Note 15e) 727    
Transfers to financial assets (27)    
Transfers to intangible assets (672)    
Provision for impairment (42)    
Ending balance 518    
Gas [member]      
Disclosure of assets recognised from costs to obtain or fulfil contracts with customers [line items]      
Effects of IFRS 15 first-time adoption (Notes 15 and 19) 90    
Additions (Note 15e) 70    
Transfers to intangible assets (78)    
Ending balance R$ 82