Document and Entity Information Document - shares	12 Months Ended
	Dec. 31, 2020	Feb. 24, 2021
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	1-7584
Entity Registrant Name	TRANSCONTINENTAL GAS PIPE LINE COMPANY, LLC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	74-1079400
Entity Address, Address Line One	2800 Post Oak Boulevard
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77056
City Area Code	713
Local Phone Number	215-2000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0000099250
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		0