EMPLOYEE STOCK BENEFIT PLANS - Summary of Stock-based Compensation Expense by Award Type (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 26.4	$ 30.4	$ 32.6
Net tax benefit related to stock-based compensation expense	(8.8)	(10.5)	(11.4)
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	7.6	7.0	6.5
Performance share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	5.8	12.7	16.1
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense	$ 13.0	$ 10.7	$ 10.0