INVESTMENTS (SUMMARY OF WEIGHTED AVERAGE LOAN-TO-VALUE RATIO FOR OUTSTANDING MORTGAGE LOANS) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	$ 1,768.0	$ 1,721.0
Carrying value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	1,768.0
Estimate of fair value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	1,800.1
Collateral	3,505.8
Less than 60% [Member] | Carrying value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	976.5
Less than 60% [Member] | Estimate of fair value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	1,004.2
Collateral	$ 2,393.0
Less than 60% [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	60.00%
60% to 70% [Member] | Carrying value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	$ 394.7
60% to 70% [Member] | Estimate of fair value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	396.7
Collateral	$ 596.2
60% to 70% [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	60.00%
60% to 70% [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	70.00%
Greater than 70% to 80% [Member] | Carrying value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	$ 282.3
Greater than 70% to 80% [Member] | Estimate of fair value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	286.2
Collateral	$ 385.1
Greater than 70% to 80% [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	70.00%
Greater than 70% to 80% [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	80.00%
Greater than 80% to 90% [Member] | Carrying value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	$ 75.3
Greater than 80% to 90% [Member] | Estimate of fair value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	74.0
Collateral	$ 89.5
Greater than 80% to 90% [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	80.00%
Greater than 80% to 90% [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	90.00%
Greater than 90% [Member] | Carrying value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	$ 39.2
Greater than 90% [Member] | Estimate of fair value [Member]
Schedule of Available-for-sale Securities [Line Items]
Mortgage loans	39.0
Collateral	$ 42.0
Greater than 90% [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Loan to value ratio	90.00%