INCOME TAXES - COMPONENTS OF DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Expected tax at statutory federal tax rates	21.00%		35.00%	21.00%	21.00%	35.00%
Estimated tax benefit related to the remeasurement of deferred taxes from tax legislation		$ 444.7
Deferred tax assets
Tax gross up - regulatory items				$ 103.2	$ 105.5
Other				14.5	23.9
Total deferred tax assets				117.7	129.4
Deferred income tax liabilities
Property-related				679.4	588.1
Employee benefits and compensation				43.3	40.9
Other				49.6	21.2
Total deferred tax liabilities				772.3	650.2
Deferred tax liability, net				$ 654.6	$ 520.8