Debt (Narrative) (Details) (USD $)		1 Months Ended	12 Months Ended			1 Months Ended			12 Months Ended	1 Months Ended
	Dec. 31, 2011	Nov. 30, 2011 CNA [Member]	Dec. 31, 2011 CNA [Member]	Dec. 31, 2011 HighMount [Member]	Dec. 31, 2011 Boardwalk Pipeline [Member]	Dec. 31, 2011 H P Storage [Member]	Feb. 28, 2011 5.75% Notes Due 2021 [Member] CNA [Member]	Dec. 31, 2011 5.5% Notes Due 2013 [Member]	Dec. 31, 2011 5.5% Notes Due 2013 [Member] Boardwalk Pipeline [Member]	Feb. 28, 2011 6.0% Notes Due 2011 [Member] CNA [Member]	Jan. 31, 2011 4.5% Notes Due February 1, 2021 [Member] Boardwalk Pipeline [Member]	Jun. 30, 2011 4.5% Notes Due February 1, 2021 [Member] Boardwalk Pipeline [Member]
Debt Disclosure [Line Items]
Maximum borrowing capacity under revolving credit facilities			$ 250,000,000	$ 250,000,000	$ 950,000,000
Debt maturity date		April 29, 2034	August 1, 2012	July 2012		December 1, 2016	August 15, 2021		April 1, 2013		February 1, 2021
Variable interest rate loan				600,000,000		200,000,000
Remaining borrowing capacity under revolving credit facilities			250,000,000
Notional amount of interest rate swaps				300,000,000
Interest rate on the hedged portion of the term loan				1.10%
Cash received from Company to utilize in refinancing of debt				400,000,000
Repayment of variable rate term loan				1,100,000,000
Face amount of debt issued							400,000,000		250,000,000		325,000,000	115,000,000
Stated interest rate							5.75%	5.50%	5.50%	6.00%	4.50%
Amount of debt redeemed		31,000,000								400,000,000
Revolving credit facility amount outstanding				100,000,000	458,000,000
Credit facility interest rate					0.50%
Credit facility maturity date					June 29, 2012
Aggregate of long term debt maturing, 2012	88,000,000
Aggregate of long term debt maturing, 2013	689,000,000
Aggregate of long term debt maturing, 2014	819,000,000
Aggregate of long term debt maturing, 2015	948,000,000
Aggregate of long term debt maturing, 2016	1,900,000,000
Aggregate of long term debt maturing, Thereafter	$ 4,600,000,000