EMPLOYEE BENEFITS - PLAN ASSETS (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 859.4	$ 816.3	$ 747.5
Pension Plan | Level 1, 2, and 3
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	411.0	414.3
Pension Plan | Level 1, 2, and 3 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	123.8	124.2
Pension Plan | Level 1, 2, and 3 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	94.7	97.3
Pension Plan | Level 1, 2, and 3 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	165.4	166.3
Pension Plan | Level 1, 2, and 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	27.1	26.5
Pension Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	218.5	221.5
Pension Plan | Level 1 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	123.8	124.2
Pension Plan | Level 1 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	94.7	97.3
Pension Plan | Level 1 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 1 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	192.5	192.8
Pension Plan | Level 2 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 2 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 2 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	165.4	166.3
Pension Plan | Level 2 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	27.1	26.5
Pension Plan | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 3 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 3 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 3 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Level 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
Pension Plan | Investments measured at net asset value per share
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	448.4	402.0
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	303.6	288.3	$ 263.4
OPEB Plan | Level 1, 2, and 3
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	186.5	178.4
OPEB Plan | Level 1, 2, and 3 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	41.1	43.0
OPEB Plan | Level 1, 2, and 3 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	34.6	37.4
OPEB Plan | Level 1, 2, and 3 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	107.7	96.1
OPEB Plan | Level 1, 2, and 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	3.1	1.9
OPEB Plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	140.4	137.0
OPEB Plan | Level 1 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	41.1	43.0
OPEB Plan | Level 1 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	34.6	37.4
OPEB Plan | Level 1 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	64.7	56.6
OPEB Plan | Level 1 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	46.1	41.4
OPEB Plan | Level 2 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Level 2 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Level 2 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	43.0	39.5
OPEB Plan | Level 2 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	3.1	1.9
OPEB Plan | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Level 3 | United States equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Level 3 | International equity
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Level 3 | United States bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Level 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0.0	0.0
OPEB Plan | Investments measured at net asset value per share
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 117.1	$ 109.9