VARIABLE INTEREST ENTITIES (VIE Assets and Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 138.6	$ 148.1	$ 281.5	$ 197.9
Restricted cash	23.0	37.6
Receivables, trade and other, net	17.1	25.2
Due from General Partner and affiliates	92.0	59.4
Accrued receivables	42.3	77.9
Inventory	15.3	35.1
Other current assets	143.7	173.0
Property, plant and equipment, net	17,572.6	17,412.4
Intangible assets, net	274.6	280.0
Other assets, net	508.0	525.6
LIABILITIES
Due to General Partner and affiliates	160.6	190.9
Accounts payable and other	493.2	654.9
Environmental liabilities	108.3	95.8
Accrued purchases	114.0	146.1
Interest payable	122.5	98.9
Property and other taxes payable	100.5	103.7
Long-term debt	7,997.7	7,728.4
Other long-term liabilities	354.4	305.2
Variable Interest Entity, Primary Beneficiary [Member]
ASSETS
Cash and cash equivalents	116.2	108.7
Restricted cash	14.6	20.6
Receivables, trade and other, net	14.7	22.8
Due from General Partner and affiliates	85.8	51.9
Accrued receivables	41.2	77.4
Inventory	15.3	35.1
Other current assets	137.9	165.3
Property, plant and equipment, net	16,918.7	16,766.6
Intangible assets, net	274.4	279.8
Other assets, net	503.8	520.2
LIABILITIES
Due to General Partner and affiliates	128.5	123.4
Accounts payable and other	358.9	534.2
Environmental liabilities	107.9	95.7
Accrued purchases	112.9	144.1
Interest payable	8.2	8.7
Property and other taxes payable	98.1	100.5
Long-term debt	1,037.5	1,087.4
Other long-term liabilities	$ 202.8	$ 209.7