INVESTMENTS - REALIZED GAINS (LOSSES) (DETAILS) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Gain (Loss) on Investments [Abstract]
Net realized investment gains (losses)	$ 22.9	$ 5.1
Net realized investment gains, excluding impairment losses, primarily fixed maturities	27.4
Net realized investment gains, excluding impairment losses	30.8	18.4
Sales of investments	670.3	1,248.1
Gain on embedded derivative related to change in fair value of certain fixed maturity investments	3.4
Total other-than-temporary impairment losses	(7.9)	(13.3)
Aggregate amortized cost of fixed maturity securities in default or considered nonperforming	0.4
Carrying value of nonperforming fixed maturity securities	0.5
Value of sold fixed maturity investments	147.6
Gross investment losses from sale of fixed maturity investments, before tax	2.3
Investments sold at a loss	0
Continuous unrealized loss position exceeding amortized cost, percent	20.00%
Other-than-temporary impairments included in accumulated other comprehensive income	$ 10.8

Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Available-for-sale, Debt Securities

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Available for Sale Securities, Continuous Unrealized Loss Position Exceeding Amortized Cost, Percent

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Available For Sale Securities, Gross Investment Losses From Sale, Before Tax

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Available For Sale Securities, Nonperforming, Aggregate Amortized Cost

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Available For Sale Securities, Nonperforming, Carrying Value

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Available For Sale Securities, Number of Securities Sold from Previous Unrealized Loss Position

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Available For Sale Securities, Value Of Securities Sold

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Gain (Loss) on Investments Excluding Other Than Temporary Impairments and Change in Fair Value of Fixed Maturities with Embedded Derivatives

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Sales of investments during the period primarily resulting from sales of actively managed fixed maturities.

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Increase in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.

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This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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