PENSION AND POST-RETIREMENT BENEFITS - Fair Value of Asset Categories (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016 |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | $ 497.2 | $ 464 |
Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 313.3 | 303.2 |
Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 183.9 | 160.8 |
Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Group Annuity Contract [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 3 |
Group Annuity Contract [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Group Annuity Contract [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 3 |
Group Annuity Contract [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. small/mid cap equity [Member] | Common and Preferred Stock [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 18.3 | 15.5 |
U.S. small/mid cap equity [Member] | Common and Preferred Stock [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 18.3 | 15.5 |
U.S. small/mid cap equity [Member] | Common and Preferred Stock [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. small/mid cap equity [Member] | Common and Preferred Stock [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. small/mid cap equity [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 16.1 | 20 |
U.S. small/mid cap equity [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 16.1 | 20 |
U.S. small/mid cap equity [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. small/mid cap equity [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Corporate bonds [Member] | Mutual Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 17.7 | 14.3 |
Corporate bonds [Member] | Mutual Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 17.7 | 14.3 |
Corporate bonds [Member] | Mutual Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Corporate bonds [Member] | Mutual Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Corporate bonds [Member] | Fixed Income Securities [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 46.7 | 41 |
Corporate bonds [Member] | Fixed Income Securities [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Corporate bonds [Member] | Fixed Income Securities [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 46.7 | 41 |
Corporate bonds [Member] | Fixed Income Securities [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Corporate bonds [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 51.5 | 56 |
Corporate bonds [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 42.3 | 54.3 |
Corporate bonds [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 9.2 | 1.7 |
Corporate bonds [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Corporate bonds [Member] | Hedge funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 10.3 | 4.5 |
Corporate bonds [Member] | Hedge funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Corporate bonds [Member] | Hedge funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 10.3 | 4.5 |
Corporate bonds [Member] | Hedge funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Government bonds [Member] | Mutual Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 8.4 | 11.9 |
Government bonds [Member] | Mutual Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 8.4 | 11.9 |
Government bonds [Member] | Mutual Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Government bonds [Member] | Mutual Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Government bonds [Member] | Fixed Income Securities [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 15.4 | 13.9 |
Government bonds [Member] | Fixed Income Securities [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Government bonds [Member] | Fixed Income Securities [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 15.4 | 13.9 |
Government bonds [Member] | Fixed Income Securities [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Government bonds [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 55.3 | 68.4 |
Government bonds [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 44.1 | 57 |
Government bonds [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 11.2 | 11.4 |
Government bonds [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Government bonds [Member] | Hedge funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0.7 | 6.5 |
Government bonds [Member] | Hedge funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Government bonds [Member] | Hedge funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0.7 | 6.5 |
Government bonds [Member] | Hedge funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. large cap equity [Member] | Mutual Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0.1 | 0.1 |
U.S. large cap equity [Member] | Mutual Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0.1 | 0.1 |
U.S. large cap equity [Member] | Mutual Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. large cap equity [Member] | Mutual Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. large cap equity [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 78.6 | 68.8 |
U.S. large cap equity [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 68.7 | 67.5 |
U.S. large cap equity [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 9.9 | 1.3 |
U.S. large cap equity [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. large cap equity [Member] | Hedge funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 1.2 | 2.1 |
U.S. large cap equity [Member] | Hedge funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
U.S. large cap equity [Member] | Hedge funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 1.2 | 2.1 |
U.S. large cap equity [Member] | Hedge funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
International equities [Member] | Mutual Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 3.8 | 3.9 |
International equities [Member] | Mutual Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 3.8 | 3.9 |
International equities [Member] | Mutual Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
International equities [Member] | Mutual Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
International equities [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 77.9 | 67 |
International equities [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 42.8 | 34.9 |
International equities [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 35.1 | 32.1 |
International equities [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Emerging markets international equity [Member] | Mutual Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 7.4 | 6.3 |
Emerging markets international equity [Member] | Mutual Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 7.4 | 6.3 |
Emerging markets international equity [Member] | Mutual Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Emerging markets international equity [Member] | Mutual Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Emerging markets international equity [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 18.9 | 15.3 |
Emerging markets international equity [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 12.8 | 9.4 |
Emerging markets international equity [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 6.1 | 5.9 |
Emerging markets international equity [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Cash and cash equivalents [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 8.2 | 10.6 |
Cash and cash equivalents [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 8.2 | 10.6 |
Cash and cash equivalents [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Cash and cash equivalents [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Cash and cash equivalents [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 13 | 4.8 |
Cash and cash equivalents [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 13 | 4.8 |
Cash and cash equivalents [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Cash and cash equivalents [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Cash and cash equivalents [Member] | Hedge funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 3.3 | 2.4 |
Cash and cash equivalents [Member] | Hedge funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 3.3 | 0 |
Cash and cash equivalents [Member] | Hedge funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 2.4 |
Cash and cash equivalents [Member] | Hedge funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Other [Member] | Mutual Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 4.5 | 3 |
Other [Member] | Mutual Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 4.5 | 3 |
Other [Member] | Mutual Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Other [Member] | Mutual Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Other [Member] | Common and Collective Funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 6.6 | (7.2) |
Other [Member] | Common and Collective Funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 1.8 | (10.3) |
Other [Member] | Common and Collective Funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 4.8 | 3.1 |
Other [Member] | Common and Collective Funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Other [Member] | Hedge funds [Member] | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 33.3 | 31.9 |
Other [Member] | Hedge funds [Member] | Level 1 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Other [Member] | Hedge funds [Member] | Level 2 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 33.3 | 31.9 |
Other [Member] | Hedge funds [Member] | Level 3 | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | $ 0 | $ 0 |