Acquisitions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	3 Months Ended			3 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2012 Boardwalk Louisiana Midstream [Member]	Oct. 02, 2012 Boardwalk Louisiana Midstream [Member]	Feb. 01, 2012 HP Storage [Member]	Mar. 31, 2012 Boardwalk Pipelines, LP [Member] HP Storage [Member]	Feb. 01, 2012 Boardwalk Pipelines, LP [Member] HP Storage [Member]	Jun. 30, 2013 Term loan Boardwalk Acquisition Company [Member]	Oct. 02, 2012 Term loan Boardwalk Acquisition Company [Member] Boardwalk Louisiana Midstream [Member]
Recasting Due to Accounting for Entities Under Common Control [Line Items]
Business Combination Difference Between Carrying Amount And Underlying Equity					$ 3.0
Business Acquisition, Date of Acquisition Agreement			Oct. 01, 2012			Feb. 01, 2012
Business Acquisition, Cost of Acquired Entity, Purchase Price				620.2
Debt Instrument, Face Amount								225.0	225.0
Prior Period Reclassification Adjustment	0.6	0.2	3.8
Business Acquisition, Percentage of Voting Interests Acquired							80.00%
Business Acquisition, Cost of Acquired Entity, Cash Paid							284.8
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net					$ 281.8