PARTNERS' CAPITAL (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	6 Months Ended
	Jan. 02, 2015	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014
Repayment of debt	$ 306.0		$ 306.0	$ 6.0
General Partner [Member]
Allocations from capital accounts		$ (1.4)	(1.0)
Alberta Clipper Pipeline [Member]
Carrying value of noncontrolling interest	$ 403.7	$ 0.0	$ 0.0
Percentage of interest acquired (in percentage)	66.70%
Difference between fair value of consideration and carrying value of noncontrolling interest	$ 364.0
Class E Units [Member]
Conversion ratio (in percentage)			100.00%
Redemption term			30 years
Notional value (in dollars per share)	$ 38.31		$ 38.31
Trading window used in determining the notional value	5 days
Earnings threshold determining cancellation of units			$ 265.9
Number of partnership units potentially cancellable (in shares)			1,305,142
Amount of gross income threshold resulting in special allocations			$ 40.0
Amount of gross income threshold resulting in special allocations, secondary period			$ 20.0
Class E Units [Member] | Alberta Clipper Pipeline [Member]
Fair value of equity transferred	$ 767.7
Number of units issued (in shares)	18,114,975
Sandpiper Project [Member]
Noncontrolling interest (in percentage)		37.50%	37.50%
i-Units [Member]
Allocations from capital accounts		$ (62.2)	$ (46.7)