INVESTMENTS - NET REALIZED INVESTMENT GAINS (LOSSES) (DETAILS) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gain (Loss) on Investments [Line Items]
Realized gains on sale	$ 115.4	$ 183.1	$ 347.1
Realized losses on sale	(15.4)	(59.9)	(147.7)
Total other-than-temporary impairment losses	(1.0)	(19.2)	(94.8)
Other-than-temporary impairment losses recognized in accumulated other comprehensive income (loss)	0	5.3	(4.7)
Net impairment losses recognized	37.8	34.6	149.8
Total realized gains	81.1	61.8	30.2
Total Fixed Maturities, Available For Sale [Member]
Gain (Loss) on Investments [Line Items]
Net impairment losses recognized	1.0	13.9	99.5
Total realized gains	99.0	109.3	99.9
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Total realized gains	0.1	(0.2)	0.1
Mortgage Loan [Member]
Gain (Loss) on Investments [Line Items]
Total realized gains	(3.7)	(29.3)	(16.9)
Impairments of Mortgage Loans And Other Investments [Member]
Gain (Loss) on Investments [Line Items]
Total realized gains	(36.8)	(20.7)	(50.3)
Other Securities [Member]
Gain (Loss) on Investments [Line Items]
Total realized gains	$ 22.5	$ 2.7	$ (2.6)