PREFERRED STOCK - Repurchases of Depository Shares of Mandatory Convertible Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended									12 Months Ended
	Nov. 30, 2017	Sep. 30, 2017	Aug. 31, 2017	Jun. 30, 2017	May 31, 2017	Apr. 30, 2017	Mar. 31, 2017	Feb. 28, 2017	Jan. 31, 2017	Dec. 31, 2017
Equity [Abstract]
Number of Depository Shares Repurchased	65,000	25,000	120,000	35,000	65,000	75,500	5,006	40,694	100,000	531,200
Amount Paid for Repurchases	$ 3.4	$ 1.4	$ 7.3	$ 2.3	$ 4.7	$ 5.5	$ 0.3	$ 2.7	$ 6.6	$ 34.2
Average Price Paid per Share	$ 51.88	$ 56.75	$ 60.65	$ 67.00	$ 72.44	$ 73.00	$ 70.00	$ 65.57	$ 65.51	$ 64.39