CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN PARTNERS' CAPITAL (Unaudited) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Adjustments to Partners' Capital [Abstract]
Net Income	$ 59.0	$ 47.2	$ 216.7	$ 145.4
Distributions paid			350.6	312.1
Sale of common units, net of related transaction costs			556.3	170.0
Capital contribution from general partner			11.8	3.6
Boardwalk HP Storage Predecessor Equity			(281.8)
Excess purchase price over net acquired assets	(3.0)		(3.0)
Other comprehensive loss			(11.4)	(0.9)
Ending Balance	3,625.0	3,247.4	3,625.0	3,247.4	3,487.0	3,241.4
Boardwalk HP Storage Predecessor Equity [Member]
Adjustments to Partners' Capital [Abstract]
Net Income			0.2	0
Distributions paid			0	0
Sale of common units, net of related transaction costs			0	0
Capital contribution from general partner			0	0
Boardwalk HP Storage Predecessor Equity			(281.8)
Excess purchase price over net acquired assets	0		0
Other comprehensive loss			0	0
Ending Balance	0	0	0	0	281.6	0
Accumulated Other Comprehensive Loss [Member]
Adjustments to Partners' Capital [Abstract]
Net Income			0	0
Distributions paid			0	0
Sale of common units, net of related transaction costs			0	0
Capital contribution from general partner			0	0
Boardwalk HP Storage Predecessor Equity			0
Excess purchase price over net acquired assets	0		0
Other comprehensive loss			(11.4)	(0.9)
Ending Balance	(60.8)	(40.4)	(60.8)	(40.4)	(49.4)	(39.5)
Common Units [Member]
Adjustments to Partners' Capital [Abstract]
Net Income			170.1	111.7
Distributions paid			301.2	269.0
Sale of common units, net of related transaction costs			556.3	170.0
Capital contribution from general partner			0	0
Boardwalk HP Storage Predecessor Equity			0
Excess purchase price over net acquired assets	(2.6)		(2.6)
Other comprehensive loss			0	0
Ending Balance	2,936.7	2,547.1	2,936.7	2,547.1	2,514.1	2,534.4
Class B Units [Member]
Adjustments to Partners' Capital [Abstract]
Net Income			20.5	14.8
Distributions paid			20.5	20.6
Sale of common units, net of related transaction costs			0	0
Capital contribution from general partner			0	0
Boardwalk HP Storage Predecessor Equity			0
Excess purchase price over net acquired assets	(0.3)		(0.3)
Other comprehensive loss			0	0
Ending Balance	678.4	677.8	678.4	677.8	678.7	683.6
General Partner [Member]
Adjustments to Partners' Capital [Abstract]
Net Income			25.9	18.9
Distributions paid			28.9	22.5
Sale of common units, net of related transaction costs			0	0
Capital contribution from general partner			11.8	3.6
Boardwalk HP Storage Predecessor Equity			0
Excess purchase price over net acquired assets	(0.1)		(0.1)
Other comprehensive loss			0	0
Ending Balance	$ 70.7	$ 62.9	$ 70.7	$ 62.9	$ 62.0	$ 62.9