XML 77 R1.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
DEI Document - USD ($)
shares in Millions, $ in Millions
 3 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Document Information [Line Items]    
Other revenue $ 46 $ 44
Defined Benefit Plan, Other Cost (Credit) $ 65 $ 64
Entity Registrant Name Tennessee Valley Authority  
Entity Central Index Key 0001376986  
Current Fiscal Year End Date --09-30  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Document Type 10-Q  
Document Period End Date Dec. 31, 2019  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Entity Common Stock, Shares Outstanding 0  
Entity Current Reporting Status Yes  
Entity Shell Company false