STOCKHOLDERS' EQUITY - Narrative (Details) - USD ($)		12 Months Ended
	Jan. 29, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Number of shares issued (in shares)		850,000	250,000
Redemption period		90 days
Redemption price per share (in dollars per share)		$ 1,000
Cost of stock repurchase		$ 1,025,000,000	$ 820,000,000	$ 430,000,000
Treasury stock purchased (in shares)		25,773,807	22,362,401
Treasury stock purchased, price per share (in dollars per share)		$ 39.77	$ 36.67
Treasury stock purchased		$ 1,025,000,000	$ 820,000,000	430,000,000
Treasury Stock, at Cost
Class of Stock [Line Items]
Treasury stock purchased		1,025,000,000	845,000,000	405,000,000
Additional Paid-in Capital
Class of Stock [Line Items]
Treasury stock purchased		$ 0	$ (25,000,000)	$ 25,000,000
Deferred compensation, share-based payments
Class of Stock [Line Items]
Shares repurchased (in shares)		0	0
Subsequent Event
Class of Stock [Line Items]
Redemption period	90 days
Series D Preferred Stock | Subsequent Event
Class of Stock [Line Items]
Preferred stock issued	$ 300,000,000
Number of shares issued (in shares)	12,000,000
Percentage interest in shares	2.50%
Preferred stock, dividend rate	6.35%
Preferred stock, liquidation preference (in dollars per share)	$ 1,000
Shares issued (in dollars per share)	$ 25
Proceeds from issuance of stock	$ 293,000,000
Redemption price per share (in dollars per share)	$ 1,000
LIBOR | Series D Preferred Stock | Subsequent Event
Class of Stock [Line Items]
Basis spread on variable rate	3.642%