SUPPLEMENTAL CASH FLOW INFORMATION - SUPPLEMENTAL INFORMATION (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Supplemental cash flow information
Cash paid for interest, net of amount capitalized			$ 252.4	$ 247.9
Cash paid (received) for income taxes, net			(10.0)	15.1
Significant non-cash investing and financing transactions
Accounts payable related to construction costs			136.9	137.3
Non-cash capital contributions from noncontrolling interest	$ 5.5	$ 4.8	$ 0.0	$ 10.2

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

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