Investments (Amortized Cost And Fair Value Of Available-For-Sale Fixed Maturities, Cost And Fair Value Of Equity Securities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	$ 6,141.2	$ 6,008.7
Fixed maturities, Gross Unrealized Gains	360.1	331.0
Fixed maturities, Gross Unrealized Losses	30.7	55.0
Fixed maturities, Fair Value	6,470.6	6,284.7
Fixed maturities, OTTI Unrealized Losses	16.3	19.9
Equity securities, Amortized Cost or Cost	315.5	239.9
Equity securities, Gross Unrealized Gains	25.5	15.3
Equity securities, Gross Unrealized Losses	6.9	8.8
Equity securities, Fair Value	334.1	246.4
U.S. Treasury And Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	224.4	261.7
Fixed maturities, Gross Unrealized Gains	6.9	7.8
Fixed maturities, Gross Unrealized Losses	0.3	0.2
Fixed maturities, Fair Value	231.0	269.3
Foreign Governments [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	273.3	239.1
Fixed maturities, Gross Unrealized Gains	0.6	0.4
Fixed maturities, Gross Unrealized Losses	0.1	0.5
Fixed maturities, Fair Value	273.8	239.0
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	3,345.9	3,218.2
Fixed maturities, Gross Unrealized Gains	218.4	197.7
Fixed maturities, Gross Unrealized Losses	18.7	40.3
Fixed maturities, Fair Value	3,545.6	3,375.6
Fixed maturities, OTTI Unrealized Losses	10.6	13.8
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	933.3	964.5
Fixed maturities, Gross Unrealized Gains	74.6	67.4
Fixed maturities, Gross Unrealized Losses	2.9	3.9
Fixed maturities, Fair Value	1,005.0	1,028.0
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	778.1	816.1
Fixed maturities, Gross Unrealized Gains	40.7	40.9
Fixed maturities, Gross Unrealized Losses	7.4	8.4
Fixed maturities, Fair Value	811.4	848.6
Fixed maturities, OTTI Unrealized Losses	5.7	6.1
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	373.1	367.6
Fixed maturities, Gross Unrealized Gains	14.6	12.5
Fixed maturities, Gross Unrealized Losses	0.3	1.0
Fixed maturities, Fair Value	387.4	379.1
Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, Amortized Cost or Cost	213.1	141.5
Fixed maturities, Gross Unrealized Gains	4.3	4.3
Fixed maturities, Gross Unrealized Losses	1.0	0.7
Fixed maturities, Fair Value	$ 216.4	$ 145.1

Available For Sale Securities OTTI Unrealized Loss

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Equity Securities, Excluding Discontinued Operations, Gross Unrealized Gains

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This item represents the total of all debt securities grouped by maturity dates, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are classified neither as held-to-maturity nor trading securities.

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For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

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