PARTNERS' CAPITAL (Distribution to Partners) (Details) - USD ($) $ / shares in Units, $ in Millions				1 Months Ended										12 Months Ended
		Feb. 12, 2016	Nov. 13, 2015	Nov. 14, 2016	Aug. 12, 2016	May 13, 2016	Aug. 14, 2015	May 15, 2015	Feb. 13, 2015	Nov. 14, 2014	Aug. 14, 2014	May 15, 2014	Feb. 14, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Distribution per Unit														$ 2.33	$ 2.31	$ 2.20
Cash available for distribution														$ 1,047.0	$ 1,000.4	$ 874.7
Amount of distribution														813.8	791.4	731.0
Cash distribution made to member or limited partner														864.2	835.9	727.8
I Units [Member]
Amount of distribution	[1]													$ 179.1	$ 161.2	$ 143.9
Units issued in lieu of cash distributions														8,571,429	4,980,552	4,562,088
General Partner [Member]
Cash distribution made to member or limited partner	[2]													$ 3.7	$ 3.3	$ 3.0
First Quarter Distribution [Member]
Distribution declaration date														Jan. 29, 2016	Jan. 29, 2015	Jan. 30, 2014
Distribution record date														Feb. 05, 2016	Feb. 06, 2015	Feb. 07, 2014
Distribution payment date														Feb. 12, 2016	Feb. 13, 2015	Feb. 14, 2014
Distribution per Unit		$ 0.5830							$ 0.5700				$ 0.5435
Cash available for distribution		$ 259.6							$ 233.9				$ 213.7
Cash distribution made to member or limited partner		216.0							194.2				178.4
First Quarter Distribution [Member] | I Units [Member]
Amount of distribution	[1]	42.7							38.9				34.6
First Quarter Distribution [Member] | General Partner [Member]
Cash distribution made to member or limited partner	[2]	$ 0.9							$ 0.8				$ 0.7
Second Quarter Distribution [Member]
Distribution declaration date														Apr. 29, 2016	Apr. 30, 2015	Apr. 30, 2014
Distribution record date														May 06, 2016	May 08, 2015	May 08, 2014
Distribution payment date														May 13, 2016	May 15, 2015	May 15, 2014
Distribution per Unit						$ 0.5830		$ 0.5700				$ 0.5435
Cash available for distribution						$ 261.2		$ 249.9				$ 214.5
Cash distribution made to member or limited partner						216.0		209.6				178.5
Second Quarter Distribution [Member] | I Units [Member]
Amount of distribution	[1]					44.3		39.5				35.3
Second Quarter Distribution [Member] | General Partner [Member]
Cash distribution made to member or limited partner	[2]					$ 0.9		$ 0.8				$ 0.7
Third Quarter Distribution [Member]
Distribution declaration date														Jul. 28, 2016	Jul. 30, 2015	Jul. 31, 2014
Distribution record date														Aug. 05, 2016	Aug. 07, 2015	Aug. 07, 2014
Distribution payment date														Aug. 12, 2016	Aug. 14, 2015	Aug. 14, 2014
Distribution per Unit					$ 0.5830		$ 0.5830				$ 0.5550
Cash available for distribution					$ 262.5		$ 257.9				$ 224.7
Cash distribution made to member or limited partner					216.1		216.1				187.2
Third Quarter Distribution [Member] | I Units [Member]
Amount of distribution	[1]				45.5		41.0				36.7
Third Quarter Distribution [Member] | General Partner [Member]
Cash distribution made to member or limited partner	[2]				$ 0.9		$ 0.8				$ 0.8
Fourth Quarter Distribution [Member]
Distribution declaration date														Oct. 28, 2016	Oct. 30, 2015	Oct. 31, 2014
Distribution record date														Nov. 07, 2016	Nov. 06, 2015	Nov. 07, 2014
Distribution payment date														Nov. 14, 2016	Nov. 13, 2015	Nov. 14, 2014
Distribution per Unit			$ 0.5830	$ 0.5830						$ 0.5550
Cash available for distribution			$ 258.7	$ 263.7						$ 221.8
Cash distribution made to member or limited partner			216.0	216.1						183.7
Fourth Quarter Distribution [Member] | I Units [Member]
Amount of distribution	[1]		41.8	46.6						37.3
Fourth Quarter Distribution [Member] | General Partner [Member]
Cash distribution made to member or limited partner	[2]		$ 0.9	$ 1.0						$ 0.8

[1] We issued 8,571,429, 4,980,552 and 4,562,088 i-units to Enbridge Management, L.L.C., the sole owner of our i-units, during 2016, 2015 and 2014, respectively, in lieu of cash distributions.

[2] We retained an amount equal to 2% of the i-unit distribution from our General Partner to maintain its 2% general partner interest in us.