STOCKHOLDERS' EQUITY - Capital Stock Information (Details) - USD ($)	3 Months Ended													12 Months Ended			23 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2016	Jul. 12, 2018	Feb. 16, 2018	Sep. 06, 2017	May 30, 2017	Feb. 16, 2017	Dec. 31, 2015	Feb. 17, 2015
Common stock, shares issued (in shares)		81,300,000				130,400,000								81,300,000	130,400,000
Common Stock, unissued shares (in shares)		218,700,000												218,700,000
Number of common stock retired														50,000,000
Common stock retired, value														$ 0
Shares of common stock in treasury (in shares)		11,700,000				50,200,000								11,700,000	50,200,000
Value of treasury stock on an average cost basis (in dollars)		$ 401,800,000				$ 1,857,700,000								$ 401,800,000	$ 1,857,700,000
Preferred stock, shares authorized (in shares)		50,000,000												50,000,000
Preferred stock, par value per share (in dollars per share)		$ 0.01												$ 0.01
Preferred stock, shares outstanding (in shares)		0				0								0	0
Stock Repurchase Program, Authorized Amount																		$ 300,000,000	$ 325,000,000	$ 225,000,000	$ 280,000,000	$ 350,000,000		$ 200,000,000
Stock Repurchased During Period, Value																	$ 131,000,000
Acquisition of Treasury Stock														$ 427,800,000	$ 926,600,000	$ 84,300,000
Common Stock, Dividends, Per Share, Cash Paid		$ 0.1	$ 0.1	$ 0.1	$ 0.10	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.07	$ 0.07	$ 0.07	$ 0.07
Common Stock
Common stock, shares outstanding (in shares)		69,600,000				80,200,000				105,000,000				69,600,000	80,200,000	105,000,000	105,000,000						107,700,000
Common stock retired, value														$ 500,000
Shares of common stock in treasury (in shares)		11,700,000												11,700,000
Acquisition of Treasury Stock (in shares)														11,500,000	25,800,000	3,600,000
Acquisition of Treasury Stock														$ 0	$ 0	$ 0
Additional Paid-in Capital
Common stock retired, value														549,200,000
Acquisition of Treasury Stock														0	0	0
Retained Earnings
Common stock retired, value														1,332,300,000
Acquisition of Treasury Stock														0	0	0
Common Stock in Treasury
Common stock retired, value														(1,882,000,000)
Acquisition of Treasury Stock														$ 427,800,000	$ 926,600,000	$ 84,300,000
Stock Options and Restricted Stock
Common Stock reserved for contingently issuable shares (in shares)		3,000,000												3,000,000
All Company Stock Plans
Number of common shares held in rabbi trust (in shares)		800,000												800,000
Value of common shares held in rabbi trust (in dollars)		$ 19,600,000												$ 19,600,000
Share repurchase program approved by Board of Directors [Member]
Acquisition of Treasury Stock (in shares)														11,400,000	25,700,000	3,500,000
Acquisition of Treasury Stock														$ 425,000,000	$ 923,700,000	$ 81,300,000
Subsequent Event
Common stock dividends declared (in dollars per share)	$ 0.11