Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	$ 2.1	$ (2.2)	$ 4.2	$ 5.9
Percent of general partner interest owned by holding company	2.00%	2.00%	2.00%	2.00%
Cash dividends paid to parent company	72.3	71.2	144.6	141.6
Boardwalk Bluegrass and Boardwalk Moss Lake [Member] \| Boardwalk Pipeline Partners, LP [Member]
Related Party Transaction [Line Items]
Variable Interest Entity, Financial or Other Support, Amount	10.0		10.0
Boardwalk Bluegrass and Boardwalk Moss Lake [Member] \| Boardwalk Pipelines Holding Company [Member]
Related Party Transaction [Line Items]
Variable Interest Entity, Financial or Other Support, Amount	$ 100.0		$ 19.7

The amount of financial or other support the reporting entity has provided (explicitly or implicitly) to the Variable Interest Entity (VIE) that it was not previously contractually required to provide or that the reporting entity intends to provide, including, for example, situations in which the reporting entity assisted the VIE in obtaining another type of support.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 810

-SubTopic 10

-Section 50

-Paragraph 5A

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7880789&loc=SL6759159-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS140-4/FIN46(R)-8

-Paragraph C4

-Subparagraph c

-Clause 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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