DEBT (Revolving Credit Facility) (Details) - USD ($)	Jun. 19, 2015	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Line of Credit Facility [Line Items]
Short-term Debt				$ 100,000,000
Letters of credit issued		$ 3,900,000	$ 3,800,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 2,000,000,000
Line of Credit Facility, term (in years)	5 years
Line of Credit, Current		$ 0	$ 0
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 70,000,000
Swingline Loans [Member]
Line of Credit Facility [Line Items]
Revolving credit facility, maximum borrowing capacity	$ 50,000,000.0
Minimum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Commitment fee rate	0.085%
Minimum [Member] | Rate 2C [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Maximum [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Commitment fee rate	0.20%
Maximum [Member] | Rate 2C [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Rate 1 [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.875%
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member] | Rate 1 [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Federal Funds Purchased [Member] | Rate 2B [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
One Month LIBOR [Member] | Rate 2C [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%