PROPERTY, PLANT AND EQUIPMENT - (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 15,559,667,000	$ 15,078,497,000
Accumulated depreciation and amortization	(2,861,541,000)	(2,507,094,000)
Property, Plant and Equipment, Net	12,698,126,000	12,571,403,000
Construction in Progress Expenditures Incurred but Not yet Paid	92,400,000	83,000,000	$ 115,700,000
Impairment of long-lived assets	15,970,000	0	83,673,000
Equity Method Investment, Other than Temporary Impairment	4,270,000	0	180,583,000
Natural Gas Gathering And Processing
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets			63,500,000
Natural Gas Gathering And Processing and Natural Gas Liquids [Member]
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets			20,200,000
Natural Gas Gathering And Processing
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	15,970,000.0	0.0	73,681,000.0
Equity Method Investment, Other than Temporary Impairment			180,583,000
Natural Gas Liquids
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	0.0	0.0	9,992,000.0
Equity Method Investment, Other than Temporary Impairment			$ 0
Non-Regulated Property, Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	(1,888,010,000)	(1,641,490,000)
Non-Regulated Property, Plant and Equipment [Member] | Gathering pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 3,613,344,000	3,352,963,000
Non-Regulated Property, Plant and Equipment [Member] | Gathering pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Non-Regulated Property, Plant and Equipment [Member] | Gathering pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Non-Regulated Property, Plant and Equipment [Member] | Processing and fractionation and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 3,873,709,000	3,831,966,000
Non-Regulated Property, Plant and Equipment [Member] | Processing and fractionation and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Non-Regulated Property, Plant and Equipment [Member] | Processing and fractionation and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Non-Regulated Property, Plant and Equipment [Member] | Storage and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 604,656,000	558,695,000
Non-Regulated Property, Plant and Equipment [Member] | Storage and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Non-Regulated Property, Plant and Equipment [Member] | Storage and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	54 years
Non-Regulated Property, Plant and Equipment [Member] | Transmission pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 700,455,000	689,804,000
Non-Regulated Property, Plant and Equipment [Member] | Transmission pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Non-Regulated Property, Plant and Equipment [Member] | Transmission pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	54 years
Non-Regulated Property, Plant and Equipment [Member] | General plant and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 504,610,000	487,559,000
Non-Regulated Property, Plant and Equipment [Member] | General plant and other | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Non-Regulated Property, Plant and Equipment [Member] | General plant and other | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	60 years
Non-Regulated Property, Plant and Equipment [Member] | Construction work in process
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 362,253,000	371,628,000
Regulated Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (973,531,000)	$ (865,604,000)
Regulated Property Plant and Equipment [Member] | Natural Gas Liquids
Property, Plant and Equipment [Line Items]
Average Depreciation Rate	1.90%	1.90%	1.90%
Regulated Property Plant and Equipment [Member] | Natural Gas Pipelines
Property, Plant and Equipment [Line Items]
Average Depreciation Rate	2.10%	2.10%	2.10%
Regulated Property Plant and Equipment [Member] | Storage and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 12,486,000	$ 13,524,000
Regulated Property Plant and Equipment [Member] | Storage and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Regulated Property Plant and Equipment [Member] | Storage and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Regulated Property Plant and Equipment [Member] | General plant and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 57,902,000	54,643,000
Regulated Property Plant and Equipment [Member] | General plant and other | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Regulated Property Plant and Equipment [Member] | General plant and other | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Regulated Property Plant and Equipment [Member] | Construction work in process
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 83,044,000	62,634,000
Regulated Property Plant and Equipment [Member] | Natural gas transmission pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,406,780,000	1,345,740,000
Regulated Property Plant and Equipment [Member] | Natural gas transmission pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Regulated Property Plant and Equipment [Member] | Natural gas transmission pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	77 years
Regulated Property Plant and Equipment [Member] | Natural gas liquids transmission pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 4,340,428,000	$ 4,309,341,000
Regulated Property Plant and Equipment [Member] | Natural gas liquids transmission pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Regulated Property Plant and Equipment [Member] | Natural gas liquids transmission pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	88 years