INVESTMENTS (SCHEDULE OF INVESTMENTS IN OUR PORTFOLIO RATED BELOW-INVESTMENT GRADE WHICH HAVE BEEN CONTINUOUSLY IN AN UNREALIZED LOSS POSITION 2) (Details) $ in Millions	Dec. 31, 2016 USD ($) issuer	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Greater than 12 months, Unrealized losses	$ (84.8)	$ (97.2)
Unrealized losses, total	(194.3)	(388.5)
Greater than 12 months, Estimated fair value	1,059.8	495.0
Fair value, total	$ 4,500.6	$ 5,310.0
Non Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 6 months, Number of issuers | issuer	4
Greater than 12 months, Number of issuers | issuer	1
Less than 6 months, Cost basis	$ 53.8
Greater than 12 months, Cost basis	0.7
Cost basis, Total	54.5
Less than 6 months, Unrealized loss	(12.1)
Greater than 12 months, Unrealized losses	(0.2)
Unrealized losses, total	(12.3)
Less than 6 months, Estimated fair value	41.7
Greater than 12 months, Estimated fair value	0.5
Fair value, total	$ 42.2