Summary of Significant Accounting Policies General and Basis of Presentation (Details) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2022 USD ($) People	Mar. 31, 2021 USD ($)	Mar. 31, 2022 USD ($) People	Mar. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)
Accounting Policies [Abstract]
Population of TVA's service area \| People	10		10
Appropriation-investment power program					$ 1,000
Depreciation expense	$ 455	$ 346	$ 908	$ 691

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

Name:	us-gaap_Depreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration