SHORT-TERM AND LONG-TERM DEBT - Schedule of Credit Facilities Available (Details) - Alliance Bernstein - USD ($)	Dec. 31, 2017	Dec. 01, 2016
Revolver
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 200,000,000
AB Revolver | Total Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000,000
AB Revolver | Revolver
Line of Credit Facility [Line Items]
Maximum borrowing capacity	200,000,000
AB Revolver | Swingline
Line of Credit Facility [Line Items]
Maximum borrowing capacity	0
AB Credit Facility | Total Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	1,000,000,000
AB Credit Facility | Revolver
Line of Credit Facility [Line Items]
Maximum borrowing capacity	1,000,000,000
AB Credit Facility | Swingline
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 240,000,000