Transactions with Affiliates (Details Textual) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended		1 Months Ended	6 Months Ended
	Jun. 30, 2012 Employees	Jun. 30, 2011	Jun. 30, 2012 Employees	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Affiliated Entity [Member]	Jun. 30, 2011 Affiliated Entity [Member]	Jul. 31, 2012 Williams Partners L.P. [Member]	Jun. 30, 2012 Williams Partners L.P. [Member]	Jun. 30, 2011 Williams Partners L.P. [Member]	Jun. 30, 2012 Northwest Pipeline Services LLC [Member]	Jun. 30, 2011 Northwest Pipeline Services LLC [Member]
Related Party Transaction [Line Items]
Advances to affiliate	$ 61,462,000		$ 61,462,000		$ 52,024,000				$ 61,500,000	$ 52,000,000
Related Party Transaction, Rate			0.01%
General and administrative	17,305,000	13,694,000	33,888,000	28,503,000		21,300,000	18,000,000
Entity Number of Employees	0		0
Labor and Related Expense											33,700,000	30,900,000
Operating Revenues	106,311,000	106,576,000	217,683,000	216,495,000			12,100,000
Distributions paid			73,000,000	64,000,000				34,500,000	73,000,000	64,000,000
Capital contributions from parent			$ 2,330,000	$ 3,500,000				$ 1,200,000	$ 2,300,000	$ 3,500,000