RELATED PARTY TRANSACTIONS (Other Agreements with MEP) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Amount outstanding, letters of credit	$ 121,100,000
Omnibus Agreement [Member] | Midcoast Energy Partners, L.P. [Member]
Related Party Transaction [Line Items]
Indemnification deductible	500,000
Maximum indemnification proceeds	15,000,000
Indemnification proceeds to Affiliate	12,200,000
Financial Support Agreement [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Total other commitments	700,000,000
Financial Support Agreement [Member] | Midcoast Energy Partners, L.P. [Member]
Related Party Transaction [Line Items]
Amount outstanding, letters of credit		$ 7,500,000
Current carrying value of Guarantor obligations	39,900,000	$ 21,700,000
General And Administrative Services Transactions [Member]
Related Party Transaction [Line Items]
General And Administrative Services Reduction	$ 25,000,000