PENSION AND POST-RETIREMENT PLANS - FAIR VALUE (Details) - Qualified Pension Benefits - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension and Post-retirement Plans
Total	$ 168.9	$ 178.9	$ 172.8
Quoted Prices in Active Markets (Level 1)
Pension and Post-retirement Plans
Total	94.6	141.2
Quoted Prices in Active Markets (Level 1) | CCF Cash Deposits and Withdrawals
Pension and Post-retirement Plans
Total	6.9	19.4
Quoted Prices in Active Markets (Level 1) | U.S. large-cap
Pension and Post-retirement Plans
Total	48.6	69.5
Quoted Prices in Active Markets (Level 1) | U.S. mid- and small-cap
Pension and Post-retirement Plans
Total	28.7	35.6
Quoted Prices in Active Markets (Level 1) | International large-cap
Pension and Post-retirement Plans
Total		5.9
Quoted Prices in Active Markets (Level 1) | Emerging markets fixed income
Pension and Post-retirement Plans
Total	10.4	10.8
Significant Observable Inputs (Level 2)
Pension and Post-retirement Plans
Total	63.8	28.1
Significant Observable Inputs (Level 2) | U.S. large-cap
Pension and Post-retirement Plans
Total	15.9
Significant Observable Inputs (Level 2) | U.S. mid- and small-cap
Pension and Post-retirement Plans
Total	6.0
Significant Observable Inputs (Level 2) | International large-cap
Pension and Post-retirement Plans
Total	16.5	11.7
Significant Observable Inputs (Level 2) | International small-cap
Pension and Post-retirement Plans
Total	6.1	6.9
Significant Observable Inputs (Level 2) | U.S. Treasuries
Pension and Post-retirement Plans
Total	5.6	0.4
Significant Observable Inputs (Level 2) | Municipal bonds
Pension and Post-retirement Plans
Total	5.3	0.1
Significant Observable Inputs (Level 2) | Investment grade U.S. corporate bonds
Pension and Post-retirement Plans
Total	2.4	2.3
Significant Observable Inputs (Level 2) | High-yield U.S. corporate bonds
Pension and Post-retirement Plans
Total	6.0	6.7
Significant Unobservable Inputs (Level 3)
Pension and Post-retirement Plans
Total	10.5	9.6
Significant Unobservable Inputs (Level 3) | Real estate partnerships interests
Pension and Post-retirement Plans
Total	10.3	9.3
Significant Unobservable Inputs (Level 3) | Private equity partnership interests
Pension and Post-retirement Plans
Total	0.2	0.3
Fair Value Measurement
Pension and Post-retirement Plans
Total	168.9	178.9
Fair Value Measurement | CCF Cash Deposits and Withdrawals
Pension and Post-retirement Plans
Total	6.9	19.4
Fair Value Measurement | U.S. large-cap
Pension and Post-retirement Plans
Total	64.5	69.5
Fair Value Measurement | U.S. mid- and small-cap
Pension and Post-retirement Plans
Total	34.7	35.6
Fair Value Measurement | International large-cap
Pension and Post-retirement Plans
Total	16.5	17.6
Fair Value Measurement | International small-cap
Pension and Post-retirement Plans
Total	6.1	6.9
Fair Value Measurement | U.S. Treasuries
Pension and Post-retirement Plans
Total	5.6	0.4
Fair Value Measurement | Municipal bonds
Pension and Post-retirement Plans
Total	5.3	0.1
Fair Value Measurement | Investment grade U.S. corporate bonds
Pension and Post-retirement Plans
Total	2.4	2.3
Fair Value Measurement | High-yield U.S. corporate bonds
Pension and Post-retirement Plans
Total	6.0	6.7
Fair Value Measurement | Emerging markets fixed income
Pension and Post-retirement Plans
Total	10.4	10.8
Fair Value Measurement | Real estate partnerships interests
Pension and Post-retirement Plans
Total	10.3	9.3
Fair Value Measurement | Private equity partnership interests
Pension and Post-retirement Plans
Total	$ 0.2	$ 0.3