RETIREMENT PLANS - Fair Value of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension | United States
Defined Benefit Plan Disclosure
Total	$ 2,372.9	$ 2,292.9	$ 1,981.4
Pension | International
Defined Benefit Plan Disclosure
Total investments at fair value	1,104.0	1,014.2
Investments measured at NAV	44.0	12.9
Total	1,148.0	1,027.1	$ 925.6
Pension | International | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	26.9	28.5
Total	26.9	28.5
Pension | International | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	1,077.1	985.7
Total	1,077.1	985.7
Pension | International | Level 3
Defined Benefit Plan Disclosure
Total		0.0
Pension | International | Cash
Defined Benefit Plan Disclosure
Total investments at fair value	11.0	7.7
Pension | International | Cash | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	11.0	7.7
Pension | International | International equity
Defined Benefit Plan Disclosure
Total investments at fair value	467.0	418.1
Pension | International | International equity | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	467.0	418.1
Pension | International | Corporate bonds
Defined Benefit Plan Disclosure
Total investments at fair value	227.7	215.8
Pension | International | Corporate bonds | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	9.1	8.2
Pension | International | Corporate bonds | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	218.6	207.6
Pension | International | Government bonds
Defined Benefit Plan Disclosure
Total investments at fair value	248.7	228.4
Pension | International | Government bonds | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	6.8	12.6
Pension | International | Government bonds | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	241.9	215.8
Pension | International | Insurance company accounts
Defined Benefit Plan Disclosure
Total investments at fair value	149.6	144.2
Pension | International | Insurance company accounts | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	149.6	144.2
Pension and Postretirement Health Care Benefit Plans | United States
Defined Benefit Plan Disclosure
Total investments at fair value	1,711.8	1,911.1
Total	2,378.7	2,299.0
Pension and Postretirement Health Care Benefit Plans | United States | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	1,217.2	1,910.8
Total	1,217.2	1,910.8
Pension and Postretirement Health Care Benefit Plans | United States | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	494.6	0.3
Total	494.6	0.3
Pension and Postretirement Health Care Benefit Plans | United States | Level 3
Defined Benefit Plan Disclosure
Total	0.0	0.0
Pension and Postretirement Health Care Benefit Plans | United States | Cash
Defined Benefit Plan Disclosure
Total investments at fair value	38.3	13.2
Pension and Postretirement Health Care Benefit Plans | United States | Cash | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	38.3	13.2
Pension and Postretirement Health Care Benefit Plans | United States | Large cap equity
Defined Benefit Plan Disclosure
Total investments at fair value	610.0	785.9
Pension and Postretirement Health Care Benefit Plans | United States | Large cap equity | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	610.0	785.9
Pension and Postretirement Health Care Benefit Plans | United States | Small cap equity
Defined Benefit Plan Disclosure
Total investments at fair value	104.8	201.7
Pension and Postretirement Health Care Benefit Plans | United States | Small cap equity | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	36.5	201.7
Pension and Postretirement Health Care Benefit Plans | United States | Small cap equity | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	68.3
Pension and Postretirement Health Care Benefit Plans | United States | International equity
Defined Benefit Plan Disclosure
Total investments at fair value	138.7	350.4
Investments measured at NAV	666.9	387.9
Pension and Postretirement Health Care Benefit Plans | United States | International equity | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	95.8	350.4
Pension and Postretirement Health Care Benefit Plans | United States | International equity | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	42.9
Pension and Postretirement Health Care Benefit Plans | United States | Core fixed income
Defined Benefit Plan Disclosure
Total investments at fair value	688.1	410.0
Pension and Postretirement Health Care Benefit Plans | United States | Core fixed income | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	360.3	410.0
Pension and Postretirement Health Care Benefit Plans | United States | Core fixed income | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	327.8
Pension and Postretirement Health Care Benefit Plans | United States | High-yield bonds
Defined Benefit Plan Disclosure
Total investments at fair value	76.3	107.9
Pension and Postretirement Health Care Benefit Plans | United States | High-yield bonds | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value	76.3	107.9
Pension and Postretirement Health Care Benefit Plans | United States | Emerging markets
Defined Benefit Plan Disclosure
Total investments at fair value	55.6	41.7
Pension and Postretirement Health Care Benefit Plans | United States | Emerging markets | Level 1
Defined Benefit Plan Disclosure
Total investments at fair value		41.7
Pension and Postretirement Health Care Benefit Plans | United States | Emerging markets | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value	$ 55.6
Pension and Postretirement Health Care Benefit Plans | United States | Insurance company accounts
Defined Benefit Plan Disclosure
Total investments at fair value		0.3
Pension and Postretirement Health Care Benefit Plans | United States | Insurance company accounts | Level 2
Defined Benefit Plan Disclosure
Total investments at fair value		$ 0.3