LONG-TERM OBLIGATIONS - Schedule of Letters of Credit Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Letters of credit outstanding, amount	$ 78.7	$ 75.8
$400 Million Facility
Debt Instrument [Line Items]
Letters of credit outstanding, amount	0.0	0.0
$300 Million Facility
Debt Instrument [Line Items]
Letters of credit outstanding, amount	34.7	33.4
Bilateral Arrangements
Debt Instrument [Line Items]
Letters of credit outstanding, amount	44.0	42.4
Continuing Operations
Debt Instrument [Line Items]
Letters of credit outstanding, amount	78.7	65.4
Continuing Operations | $400 Million Facility
Debt Instrument [Line Items]
Letters of credit outstanding, amount	0.0	0.0
Continuing Operations | $300 Million Facility
Debt Instrument [Line Items]
Letters of credit outstanding, amount	34.7	33.4
Continuing Operations | Bilateral Arrangements
Debt Instrument [Line Items]
Letters of credit outstanding, amount	44.0	32.0
Discontinued Operations
Debt Instrument [Line Items]
Letters of credit outstanding, amount	0.0	10.4
Discontinued Operations | $400 Million Facility
Debt Instrument [Line Items]
Letters of credit outstanding, amount	0.0	0.0
Discontinued Operations | $300 Million Facility
Debt Instrument [Line Items]
Letters of credit outstanding, amount	0.0	0.0
Discontinued Operations | Bilateral Arrangements
Debt Instrument [Line Items]
Letters of credit outstanding, amount	$ 0.0	$ 10.4