NONCONTROLLING INTERESTS (Consolidated statements of financial position) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stockholders' Equity Attributable to Noncontrolling Interest	$ 3,846.1	$ 3,944.5	$ 3,609.0	$ 1,975.6
Eastern Access Interests [Member]
Stockholders' Equity Attributable to Noncontrolling Interest	1,891.9	1,801.1
US Mainline Expansion Interests [Member]
Stockholders' Equity Attributable to Noncontrolling Interest	1,621.4	1,476.6
North Dakota Pipeline Company Interests [Member]
Stockholders' Equity Attributable to Noncontrolling Interest	29.6	286.8
Midcoast Energy Partners, L.P. [Member]
Stockholders' Equity Attributable to Noncontrolling Interest	$ 303.2	$ 380.0