INCOME TAXES - COMPONENTS OF DEFERRED INCOME TAXES (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets
Tax gross up - regulatory items	$ 102.4	$ 106.5
Future tax benefits	8.7	33.3
Other	20.5	22.2
Total deferred tax assets	131.6	162.0
Deferred income tax liabilities
Property-related	822.1	749.1
Employee benefits and compensation	49.5	44.6
Other	42.2	51.0
Total deferred tax liabilities	913.8	844.7
Deferred tax liability, net	$ 782.2	$ 682.7