FAIR VALUE MEASUREMENTS - BALANCE SHEET RECURRING (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Interest sensitive products [Member]
Liabilities:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	$ (1,096.0)	$ (1,102.1)	$ (1,057.1)	$ (1,081.5)
Purchases, sales, issuances and settlements, net	(14.3)	(7.2)	(18.3)	(10.0)
Total realized and unrealized gains (losses) included in net income	(16.7)	35.3	(51.6)	17.5
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.0	0.0	0.0	0.0
Transfers into level 3	0.0	0.0	0.0	0.0
Transfers out of level 3	0.0	0.0	0.0	0.0
Fair value, measurement with unobservable inputs reconciliation, ending balance	(1,127.0)	(1,074.0)	(1,127.0)	(1,074.0)
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	(16.7)	35.3	(51.6)	17.5
Corporate securities [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	173.3	136.0	170.4	365.9
Purchases, sales, issuances and settlements, net	(2.6)	(6.2)	(14.4)	(26.3)
Total realized and unrealized gains (losses) included in net income	0.0	(0.9)	(7.0)	(2.2)
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	4.7	(6.0)	12.3	(6.1)
Transfers into level 3	0.0	10.8	20.3	9.1
Transfers out of level 3	(0.8)	0.0	(7.0)	(206.7)
Fair value, measurement with unobservable inputs reconciliation, ending balance	174.6	133.7	174.6	133.7
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	0.0	0.0	(5.6)	0.0
Debt securities issued by foreign governments [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	0.0		0.0
Purchases, sales, issuances and settlements, net	4.0		4.0
Total realized and unrealized gains (losses) included in net income	0.0		0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.1		0.1
Transfers into level 3	0.0		0.0
Transfers out of level 3	0.0		0.0
Fair value, measurement with unobservable inputs reconciliation, ending balance	4.1		4.1
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	0.0		0.0
States and political subdivisions [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance				35.5
Purchases, sales, issuances and settlements, net				0.0
Total realized and unrealized gains (losses) included in net income				0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)				0.0
Transfers into level 3				0.0
Transfers out of level 3				(35.5)
Fair value, measurement with unobservable inputs reconciliation, ending balance		0.0		0.0
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date				0.0
Asset-backed Securities [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	43.8	65.8	35.9	59.2
Purchases, sales, issuances and settlements, net	4.7	(1.1)	14.5	(1.9)
Total realized and unrealized gains (losses) included in net income	0.0	0.0	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	1.6	(1.8)	2.4	(0.6)
Transfers into level 3	0.0	0.0	0.0	10.0
Transfers out of level 3	(11.0)	(9.6)	(13.7)	(13.4)
Fair value, measurement with unobservable inputs reconciliation, ending balance	39.1	53.3	39.1	53.3
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	0.0	0.0	0.0	0.0
Commercial mortgage-backed securities [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	1.1	2.1	1.1	1.2
Purchases, sales, issuances and settlements, net	0.0	0.0	0.0	0.0
Total realized and unrealized gains (losses) included in net income	0.0	0.0	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.0	0.0	0.0	0.0
Transfers into level 3	0.0	0.0	0.0	0.0
Transfers out of level 3	0.0	(0.9)	0.0	0.0
Fair value, measurement with unobservable inputs reconciliation, ending balance	1.1	1.2	1.1	1.2
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	0.0	0.0	0.0	0.0
Mortgage pass-through securities [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance		0.2	0.1	0.4
Purchases, sales, issuances and settlements, net		0.0	(0.1)	(0.2)
Total realized and unrealized gains (losses) included in net income		0.0	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)		0.0	0.0	0.0
Transfers into level 3		0.0	0.0	0.0
Transfers out of level 3		0.0	0.0	0.0
Fair value, measurement with unobservable inputs reconciliation, ending balance	0.0	0.2	0.0	0.2
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date		0.0	0.0	0.0
Total fixed maturities, available for sale [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	218.2	204.1	207.5	462.2
Purchases, sales, issuances and settlements, net	6.1	(7.3)	4.0	(28.4)
Total realized and unrealized gains (losses) included in net income	0.0	(0.9)	(7.0)	(2.2)
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	6.4	(7.8)	14.8	(6.7)
Transfers into level 3	0.0	10.8	20.3	19.1
Transfers out of level 3	(11.8)	(10.5)	(20.7)	(255.6)
Fair value, measurement with unobservable inputs reconciliation, ending balance	218.9	188.4	218.9	188.4
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	0.0	0.0	(5.6)	0.0
Equity securities [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	32.4	29.0	32.0	28.0
Purchases, sales, issuances and settlements, net	1.1	0.9	2.2	1.9
Total realized and unrealized gains (losses) included in net income	(12.8)	0.0	(12.8)	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.7	0.0	0.0	0.0
Transfers into level 3	0.0	0.0	0.0	0.0
Transfers out of level 3	0.0	0.0	0.0	0.0
Fair value, measurement with unobservable inputs reconciliation, ending balance	21.4	29.9	21.4	29.9
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	(12.8)	0.0	(12.8)	0.0
Trading securities [Member]
Assets:
Fair value, measurement with unobservable inputs reconciliation, beginning balance	39.0	0.0	39.9	28.6
Purchases, sales, issuances and settlements, net	0.0	9.4	0.0	9.5
Total realized and unrealized gains (losses) included in net income	0.0	0.0	0.0	0.0
Total realized and unrealized gains (losses) included in accumulated other comprehensive income (loss)	0.0	1.9	0.0	1.8
Transfers into level 3	0.0	28.6	0.0	0.0
Transfers out of level 3	(39.0)	0.0	(39.9)	0.0
Fair value, measurement with unobservable inputs reconciliation, ending balance	0.0	39.9	0.0	39.9
Amount of total gains (losses) for the period included in our net income relating to assets and liabilities still held s of the reporting date	$ 0.0	$ 1.9	$ 0.0	$ 1.8