SEGMENT INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Operating revenues:
Transportation and other services	$ 616.4	$ 634.6	$ 1,817.6	$ 1,885.6
Total operating revenues	616.4	634.6	1,817.6	1,885.6
Operating expenses:
Environmental costs, net of recoveries	1.2	(8.7)	15.0	8.3
Operating and administrative	162.6	152.0	474.0	428.0
Power	80.1	74.3	221.0	206.8
Depreciation and amortization	111.8	109.4	328.9	315.7
Gain on sale of assets	(5.5)	0.0	(67.6)	0.0
Asset impairment	0.0	756.7	0.0	757.1
Total costs and expenses	350.2	1,083.7	971.3	1,715.9
Operating income (loss)	266.2	(449.1)	846.3	169.7
Interest expense, net	(104.1)	(103.4)	(305.8)	(301.2)
Allowance for equity used during construction	12.2	10.0	33.2	35.7
Other income	21.8	0.6	33.2	0.9
Income before income taxes	196.1	(541.9)	606.9	(94.9)
Income tax benefit (expense)	(0.1)	(1.6)	0.4	(5.2)
Net income from continuing operations	196.0	(543.5)	607.3	(100.1)
Loss from discontinued operations, net of tax	0.0	(31.1)	(56.8)	(124.4)
Net income (loss)	196.0	(574.6)	550.5	(224.5)
Total Assets
Assets	14,738.2		14,738.2		$ 18,110.1
Liquids [Member]
Operating revenues:
Transportation and other services	616.4	634.6	1,817.6	1,885.6
Total operating revenues	616.4	634.6	1,817.6	1,885.6
Operating expenses:
Environmental costs, net of recoveries	1.2	(8.7)	15.0	8.3
Operating and administrative	160.9	149.7	464.9	418.6
Power	80.1	74.3	221.0	206.8
Depreciation and amortization	111.8	109.4	328.9	315.7
Gain on sale of assets	(5.5)		(67.6)
Asset impairment		756.7		757.1
Total costs and expenses	348.5	1,081.4	962.2	1,706.5
Operating income (loss)	267.9	(446.8)	855.4	179.1
Other income	21.7		28.1
Loss from discontinued operations, net of tax		0.0	0.0	0.0
Natural Gas [Member]
Operating revenues:
Transportation and other services	0.0	0.0	0.0	0.0
Total operating revenues	0.0	0.0	0.0	0.0
Operating expenses:
Environmental costs, net of recoveries	0.0	0.0	0.0	0.0
Operating and administrative	0.0	0.0	0.0	0.0
Power	0.0	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0	0.0
Gain on sale of assets	0.0		0.0
Asset impairment		0.0		0.0
Total costs and expenses	0.0	0.0	0.0	0.0
Operating income (loss)	0.0	0.0	0.0	0.0
Other income	0.0		0.0
Loss from discontinued operations, net of tax		(20.6)	(51.1)	(96.9)
Other [Member]
Operating revenues:
Transportation and other services	0.0	0.0	0.0	0.0
Total operating revenues	0.0	0.0	0.0	0.0
Operating expenses:
Environmental costs, net of recoveries	0.0	0.0	0.0	0.0
Operating and administrative	1.7	2.3	9.1	9.4
Power	0.0	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0	0.0
Gain on sale of assets	0.0		0.0
Asset impairment		0.0		0.0
Total costs and expenses	1.7	2.3	9.1	9.4
Operating income (loss)	(1.7)	(2.3)	(9.1)	(9.4)
Other income	0.1		5.1
Loss from discontinued operations, net of tax		$ (10.5)	(5.7)	$ (27.5)
Continuing Operations [Member]
Total Assets
Assets	14,738.2		14,738.2		13,196.1
Continuing Operations [Member] | Liquids [Member]
Total Assets
Assets	14,721.5		14,721.5		13,030.5
Continuing Operations [Member] | Natural Gas [Member]
Total Assets
Assets	0.0		0.0		0.0
Continuing Operations [Member] | Other [Member]
Total Assets
Assets	$ 16.7		$ 16.7		$ 165.6