PARTNERS' CAPITAL (Components Of Net Income (Loss) Attributable To Noncontrolling Interest) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Noncontrolling interest	$ 68.8	$ 51.3
Alberta Clipper Interests [Member]
Noncontrolling interest	0.0	(0.8)
Eastern Access Interests [Member]
Noncontrolling interest	51.5	44.8
U.S. Mainline Expansion Interests [Member]
Noncontrolling interest	26.6	16.5
Midcoast Energy Partners, L.P. [Member]
Noncontrolling interest	$ (9.3)	$ (9.2)

Amount of Net Income (Loss) attributable to noncontrolling interest.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 55
-Paragraph 4J
-URI http://asc.fasb.org/extlink&oid=35736750&loc=SL4591551-111686

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=18733093&loc=SL4573702-111684

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