Investments (Current And Long-Term Investments, Available-For-Sale) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Cost or Amortized Cost	$ 18,478.5	$ 17,356.1
Gross Unrealized Gains	1,054.2	1,282.1
Gross Unrealized Losses, Less than 12 Months	(244.5)	(36.7)
Gross Unrealized Losses, 12 Months or Greater	(33.3)	(14.6)
Estimated Fair Value	19,254.9	18,586.9
Fixed Maturity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	17,282.6	16,459.1
Gross Unrealized Gains	475.3	924.1
Gross Unrealized Losses, Less than 12 Months	(236.5)	(24.2)
Gross Unrealized Losses, 12 Months or Greater	(33.3)	(14.6)
Estimated Fair Value	17,488.1	17,344.4
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	(0.8)	(3.4)
Fixed Maturity Securities [Member] \| United States Government Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	300.8	330.3
Gross Unrealized Gains	2.5	13.1
Gross Unrealized Losses, Less than 12 Months	(3.4)	(0.2)
Gross Unrealized Losses, 12 Months or Greater	0	0
Estimated Fair Value	299.9	343.2
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	0	0
Fixed Maturity Securities [Member] \| Government Sponsored Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	174.4	153.6
Gross Unrealized Gains	0.4	2.6
Gross Unrealized Losses, Less than 12 Months	(1.3)	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Estimated Fair Value	173.5	156.2
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	0	0
Fixed Maturity Securities [Member] \| States, Municipalities And Political Subdivisions - Tax-Exempt [Member]
Investment [Line Items]
Cost or Amortized Cost	5,899.5	5,501.3
Gross Unrealized Gains	202.9	388.2
Gross Unrealized Losses, Less than 12 Months	(90.1)	(5.7)
Gross Unrealized Losses, 12 Months or Greater	(9.6)	(1.6)
Estimated Fair Value	6,002.7	5,882.2
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	(0.6)	0
Fixed Maturity Securities [Member] \| Corporate Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	7,614.1	7,642.0
Gross Unrealized Gains	205.2	387.0
Gross Unrealized Losses, Less than 12 Months	(95.2)	(17.0)
Gross Unrealized Losses, 12 Months or Greater	(15.5)	(8.0)
Estimated Fair Value	7,708.6	8,004.0
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	(0.1)	(1.7)
Fixed Maturity Securities [Member] \| Options Embedded in Convertible Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	89.2	67.2
Gross Unrealized Gains	0	0
Gross Unrealized Losses, Less than 12 Months	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Estimated Fair Value	89.2	67.2
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	0	0
Fixed Maturity Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	2,269.4	2,204.7
Gross Unrealized Gains	48.0	103.1
Gross Unrealized Losses, Less than 12 Months	(41.4)	(1.1)
Gross Unrealized Losses, 12 Months or Greater	(7.1)	(1.9)
Estimated Fair Value	2,268.9	2,304.8
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	0	(0.4)
Fixed Maturity Securities [Member] \| Commercial Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	479.0	323.2
Gross Unrealized Gains	10.5	22.5
Gross Unrealized Losses, Less than 12 Months	(2.6)	0
Gross Unrealized Losses, 12 Months or Greater	(0.3)	0
Estimated Fair Value	486.6	345.7
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	0	0
Fixed Maturity Securities [Member] \| Other Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	456.2	236.8
Gross Unrealized Gains	5.8	7.6
Gross Unrealized Losses, Less than 12 Months	(2.5)	(0.2)
Gross Unrealized Losses, 12 Months or Greater	(0.8)	(3.1)
Estimated Fair Value	458.7	241.1
Non-Credit Component of Other-Than-Temporary Impairments Recognized in AOCI	(0.1)	(1.3)
Equity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	1,195.9	897.0
Gross Unrealized Gains	578.9	358.0
Gross Unrealized Losses, Less than 12 Months	(8.0)	(12.5)
Gross Unrealized Losses, 12 Months or Greater	0	0
Estimated Fair Value	$ 1,766.8	$ 1,242.5

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

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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