SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Supplemental cash flow information
Cash (paid) for interest, net of amount capitalized	$ (57.6)	$ (58.1)
Cash (paid) received for income taxes, net	(63.4)	0.6
Significant noncash transactions
Accounts payable related to construction costs	13.0	12.4
Transfer of investment in ATC
Related parties
Equity method investment transfer to affiliated company	415.4	0.0
Dividends not received transfered to affiliate			$ 13.4
UMERC transfer
Related parties
Transfer of net assets to UMERC	$ 60.0	$ 0.0

Future cash outflow to pay for purchases of fixed assets that have occurred.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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