SUBSEQUENT EVENTS (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended
	May 31, 2012	Apr. 30, 2012	May 02, 2012
Great Lakes
Subsequent events
Aggregate distribution declared and payable by investee		$ 27
Ownership interest (as a percent)			46.45%
Partnership's share of distributions declared and payable by investee	12
Northern Border
Subsequent events
Aggregate distribution declared and payable by investee		52
Ownership interest (as a percent)			50.00%
Partnership's share of distributions declared and payable by investee	26
GTN
Subsequent events
Aggregate distribution declared and payable by investee		33
Ownership interest (as a percent)			25.00%
Partnership's share of distributions declared and payable by investee	8
Bison
Subsequent events
Aggregate distribution declared and payable by investee		17
Ownership interest (as a percent)			25.00%
Partnership's share of distributions declared and payable by investee	$ 4
Cash distribution declared
Subsequent events
Cash distribution (in dollars per unit)		$ 0.77