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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - General (Details)
People in Millions, $ in Millions
12 Months Ended
Sep. 30, 2016
USD ($)
People
Customers
Population of Service Area  
Population of TVA's service area (number of people) | People 9
Maximum original maturity 3 months
Number of customers for whom unbilled revenues are estimated | Customers 6
Revenue Capitalized During Pre-Commercial Operations $ 18
Fuel Cost Capitalized During Pre-Commercial Operations 6
Recorded cost for emission allowances granted by the Environmental Protection Agency 0
Possible amount of future payments to the Department of Energy under the blended low-enriched uranium program 165
Payments attributable to blended low-enriched uranium fuel currently in use 151
BLEU fuel obligation $ 5