Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 02, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	Transcontinental Gas Pipe Line Company, LLC
Entity Central Index Key	0000099250
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		0