DEBT (Narrative) (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Oct. 06, 2015	Sep. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 28, 2016	Sep. 03, 2015
Line of Credit Facility [Line Items]
Proceeds from (Repayments of) Lines of Credit			$ 85.0	$ 80.0	$ 1,185.0
Line of Credit Facility, Maximum Borrowing Capacity			750.0
Proceeds from Issuance of Commercial Paper			1,500.0
Line of Credit Facility, Current Borrowing Capacity			2,625.0
Line of Credit Facility, Remaining Borrowing Capacity			846.3
Long-term Debt, Gross			7,927.6	8,076.1
Proceeds from Issuance of Long-term Debt, Total			0.0	1,600.0	$ 398.1
MEP Private Debt Issuance [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 1,000.0
Line of Credit Facility, Covenant Terms			The applicable margin on Eurodollar (LIBOR) rate loans ranges from 1.75% to 2.75% and the applicable margin on base rate loans ranges from 0.75% to 1.75%, in each case determined based upon our total leverage ratio (as defined below) at the applicable time.
Line of Credit Facility, Commitment Fee Description			A commitment fee is payable by MEP equal to an applicable margin times the daily unused amount of the lenders commitment, which applicable margin ranges from 0.30% to 0.50% based upon our total leverage ratio at the applicable time.
Line of Credit Facility, Collateral			(1) for two consecutive quarters, the total leverage ratio as described below, exceeds 4.25 to 1.00, or 4.75 to 1.00 during acquisition periods, (2) uncured breach to certain terms and conditions of the MEP Credit Agreement and (3) obtaining a non-investment grade initial debt rating from either S&P or Moody’s.
Line Of Credit Facility Expired Borrowing Capacity							$ 140.0
Line Of Credit Facility Additional Borrowing Capacity To Be Expired							25.0
Minimum [Member] | MEP Private Debt Issuance [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity							810.0
Maximum [Member] | MEP Private Debt Issuance [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity							$ 850.0
Senior Notes [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount		$ 400.0
Long-term Debt, Gross	$ 1,600.0		$ 200.0
Accumulated Other Comprehensive Income Amortized As Interest Expense	238.3
Payments of Debt Issuance Costs	314.7
Senior Unsecured Notes Issued, Value	1,600.0
Proceeds from Issuance of Unsecured Debt	$ 1,575.0
Senior Notes [Member] | Senior Notes due October 2020 [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Maturity Date	Oct. 15, 2020
Long-term Debt, Gross	$ 500.0
Senior Notes [Member] | 7.000% Senior Notes due October 2018 [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.00%
Long-term Debt, Gross			$ 100.0
Senior Notes [Member] | 7.125% Senior Notes due October 2028 [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.125%
Long-term Debt, Gross			$ 100.0
Junior Subordinated Debt [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			8.05%
Debt Instrument, Maturity Date			Dec. 31, 2067
Long-term Debt, Gross			$ 400.0
Debt Instrument, Description of Variable Rate Basis			interest at a variable rate equal to the three-month LIBOR for the related interest period increased by 3.7975%, payable quarterly in arrears on January 1, April 1, July 1 and October 1 of each year beginning January 1, 2018.
Midcoast Energy Partners [Member]
Line of Credit Facility [Line Items]
Proceeds from (Repayments of) Lines of Credit			$ 70.0
Proceeds from Lines of Credit			7.8
Repayments of Lines of Credit			7.9
Line of Credit Facility, Current Borrowing Capacity			670.0
Proceeds from Issuance of Long-term Debt, Total		398.1
Payments For Interest Rate Swaps		$ 0.9
Commercial Paper [Member]
Line of Credit Facility [Line Items]
Proceeds from (Repayments of) Lines of Credit			65.8
Proceeds from Lines of Credit			7,800.0
Repayments of Lines of Credit			7,700.0
Commercial paper aggregate principal amount supported by Credit Facilities			1,500.0
Fixed Rate Debt Obligations [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Fair Value Disclosure			6,500.0	$ 5,900.0
Senior Notes Due October 2025 [Member] | Senior Notes [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Maturity Date	Oct. 15, 2025
Long-term Debt, Gross	$ 500.0
Senior Notes Due October 2045 [Member] | Senior Notes [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Maturity Date	Oct. 15, 2045
Long-term Debt, Gross	$ 600.0
Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 2,000.0			$ 25.0
Line of Credit Facility, Expiration Date			Sep. 26, 2020
Credit Facility [Member] | Portion of Credit Facility Due in 2018 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 175.0
364-Day Credit Facility [Member]
Line of Credit Facility [Line Items]
Proceeds from (Repayments of) Lines of Credit			155.0
Line of Credit Facility, Maximum Borrowing Capacity			625.0
Proceeds from Lines of Credit			17,700.0
Repayments of Lines of Credit			$ 17,600.0
Debt Instrument, Term			364 days
Line of Credit Facility, Current Borrowing Capacity			$ 2,600.0
Line of Credit Facility, Remaining Borrowing Capacity			800.0
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			175.0
Standby Letters of Credit [Member] | Midcoast Energy Partners [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity			90.0
Revolving Credit Facility [Member] | Midcoast Energy Partners [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity			75.0
EUS 364-day Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 750.0