PARTNERS' CAPITAL (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended
	Jan. 02, 2015	Sep. 30, 2015	Sep. 30, 2014
Period of reset related to quarterly cash contributions		5 years
Repayment of debt	$ 306.0	$ 306.0	$ 12.0
General Partner [Member]
Allocations from capital accounts	(1.0)	(13.5)
Alberta Clipper Pipeline [Member]
Carrying value of noncontrolling interest	$ 403.7	$ 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%
i-Units [Member]
Allocations from capital accounts	$ (46.7)	$ (185.4)