Investments (Current And Long-Term Investments, Available-For-Sale) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Cost or Amortized Cost	$ 18,583.5	$ 18,951.8
Gross Unrealized Gains	815.0	1,154.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(321.5)	(139.6)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(126.0)	(57.2)
Estimated Fair Value	18,951.0	19,909.9
Fixed Maturity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	17,500.4	17,621.1
Gross Unrealized Gains	394.4	536.4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(290.6)	(128.5)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(126.0)	(57.2)
Estimated Fair Value	17,478.2	17,971.8
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(15.4)	(6.8)
Fixed Maturity Securities [Member] \| United States Government Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	349.5	315.7
Gross Unrealized Gains	2.0	4.6
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1.6)	(0.3)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.0
Estimated Fair Value	349.9	320.0
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0.0	0.0
Fixed Maturity Securities [Member] \| Government Sponsored Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	75.6	94.6
Gross Unrealized Gains	0.5	0.8
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(0.1)	0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(0.1)	(0.4)
Estimated Fair Value	75.9	95.0
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0.0	0.0
Fixed Maturity Securities [Member] \| States, Municipalities And Political Subdivisions, Tax-Exempt [Member]
Investment [Line Items]
Cost or Amortized Cost	5,976.7	5,451.4
Gross Unrealized Gains	284.1	287.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4.0)	(1.8)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(5.2)	(3.0)
Estimated Fair Value	6,251.6	5,733.6
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0.0	0.0
Fixed Maturity Securities [Member] \| Corporate Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	8,209.7	8,335.9
Gross Unrealized Gains	61.1	162.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(267.2)	(123.1)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(110.5)	(43.2)
Estimated Fair Value	7,893.1	8,332.5
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	(15.4)	(6.8)
Fixed Maturity Securities [Member] \| Options Embedded in Convertible Securities [Member]
Investment [Line Items]
Cost or Amortized Cost		98.7
Gross Unrealized Gains		0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0.0
Estimated Fair Value		98.7
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income		0.0
Fixed Maturity Securities [Member] \| Residential Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	1,724.5	2,099.7
Gross Unrealized Gains	41.2	68.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(7.6)	(1.0)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(7.2)	(8.6)
Estimated Fair Value	1,750.9	2,159.0
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0.0	0.0
Fixed Maturity Securities [Member] \| Commercial Mortgage-Backed Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	407.6	504.8
Gross Unrealized Gains	1.4	6.1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4.3)	(0.6)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(0.4)	(0.4)
Estimated Fair Value	404.3	509.9
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0.0	0.0
Fixed Maturity Securities [Member] \| Other Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	756.8	720.3
Gross Unrealized Gains	4.1	6.1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(5.8)	(1.7)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(2.6)	(1.6)
Estimated Fair Value	752.5	723.1
Non-Credit Component of Other-Than-Temporary Impairments Recognized in Accumulated Other Comprehensive Income	0.0	0.0
Equity Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	1,083.1	1,330.7
Gross Unrealized Gains	420.6	618.5
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(30.9)	(11.1)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.0
Estimated Fair Value	$ 1,472.8	$ 1,938.1

Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

+ Details

Name:	invest_InvestmentLineItems
Namespace Prefix:	invest_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

+ Details

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

+ References

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount before tax of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss, attributable to parent entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25362-111560

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParentAvailableforsaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_OptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_OtherDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: