INVESTMENTS IN VARIABLE INTEREST ENTITIES - SCHEDULE OF VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Amortized cost
Due after one year through five years	$ 1,079.1		$ 1,346.8
Due after five years through ten years	1,432.3		1,648.2
Amortized cost	18,801.6		18,107.8
Estimated fair value
Due after one year through five years	1,127.0		1,377.1
Due after five years through ten years	1,535.1		1,625.7
Total fixed maturities, available for sale	21,089.2	$ 18,443.7	$ 18,447.7
Variable Interest Entity, Primary Beneficiary
Amortized cost
Due after one year through five years	643.5
Due after five years through ten years	583.5
Amortized cost	1,227.0
Estimated fair value
Due after one year through five years	628.5
Due after five years through ten years	575.7
Total fixed maturities, available for sale	$ 1,204.2