RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES - Part 2 (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) MMcf MMBbls	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) MMcf MMBbls
Derivative [Line Items]
Notional Amount Of Cash Flow Hedge Instruments Settled | $		$ 400.0
Senior Notes, Noncurrent | $		$ 1,200.0	$ 1,200.0
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount		0		0
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount		(24,500)		(38,400)
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Purchased/Payor
Derivative [Line Items]
Notional amount		0		0
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Sold/Receiver
Derivative [Line Items]
Notional amount		(24,500)		(38,400)
Derivatives designated as hedging instruments | Put options | Natural gas (Bcf) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount		0		49,500
Derivatives designated as hedging instruments | Put options | Natural gas (Bcf) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount		0		0
Derivatives designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount | MMBbls		3.5		0.0
Derivatives designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount | MMBbls		(11.1)		(3.6)
Derivatives designated as hedging instruments | Interest Rate Contracts | Purchased/Payor
Derivative [Line Items]
Derivative, Notional Amount | $		$ 1,750.0		$ 2,150.0
Derivatives designated as hedging instruments | Interest Rate Contracts | Sold/Receiver
Derivative [Line Items]
Derivative, Notional Amount | $		$ 0.0		$ 0.0
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount		0		400
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount		0		0
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Purchased/Payor
Derivative [Line Items]
Notional amount		0		400
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Sold/Receiver
Derivative [Line Items]
Notional amount		0		0
Derivatives not designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount | MMBbls		0.8		0.5
Derivatives not designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount | MMBbls		(0.8)		(0.7)
LIBOR Based Interest Payments [Member] | Cash Flow Hedging [Member] | Forward contracts | Interest Rate Contracts
Derivative [Line Items]
Derivative, Notional Amount | $		$ 500.0		$ 1,000.0
LIBOR Based Interest Payments [Member] | Cash Flow Hedging [Member] | Forward contracts | Interest Rate Contracts | Subsequent Event [Member]
Derivative [Line Items]
Notional Amount Of Cash Flow Hedge Instruments Settled | $	$ 500.0
Forecasted Debt Issuances [Member] | Cash Flow Hedging [Member] | Forward contracts | Interest Rate Contracts
Derivative [Line Items]
Derivative, Notional Amount | $		1,300.0		$ 1,200.0
Derivative, Notional Amount, New Contracts | $		$ 500.0