Transactions with Affiliates (Details Textual) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended		1 Months Ended	9 Months Ended			9 Months Ended
	Sep. 30, 2012 Employees	Sep. 30, 2011	Sep. 30, 2012 Employees	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Affiliated Entity [Member]	Sep. 30, 2011 Affiliated Entity [Member]	Oct. 30, 2012 Williams Partners L.P. [Member]	Sep. 30, 2012 Williams Partners L.P. [Member]	Sep. 30, 2011 Williams Partners L.P. [Member]	Dec. 31, 2011 Williams Partners L.P. [Member]	Sep. 30, 2012 Northwest Pipeline Services LLC [Member]	Sep. 30, 2011 Northwest Pipeline Services LLC [Member]
Related Party Transaction [Line Items]
Advances to affiliate	$ 53,301,000		$ 53,301,000		$ 52,024,000				$ 53,300,000		$ 52,000,000
Related Party Transaction, Rate			0.01%
General and administrative	17,250,000	13,647,000	51,138,000	42,150,000		32,100,000	26,800,000
Entity Number of Employees	0		0
Labor and Related Expense												51,800,000	46,700,000
Operating Revenues	107,643,000	107,216,000	325,326,000	323,711,000			18,400,000
Distributions paid			107,500,000	94,000,000				30,000,000	107,500,000	94,000,000
Capital contributions from parent			$ 3,530,000	$ 4,400,000				$ 5,100,000	$ 3,500,000	$ 4,400,000