Document and Entity Information (USD $)	6 Months Ended
	Jun. 30, 2013	Jul. 30, 2013 Common Stock [Member]	Jul. 30, 2013 Common Class B [Member]
Entity Information [Line Items]
Entity Registrant Name	Boardwalk Pipeline Partners, LP
Entity Central Index Key	0001336047
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float	$ 3,552,657,574
Entity Common Stock, Shares Outstanding		220,357,134	22,866,667
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2013