Investments (Current And Long-Term Investments, Available-For-Sale) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Investments [Line Items]
Cost or Amortized Cost	$ 19,660.4		$ 18,478.5
Gross Unrealized Gains	1,140.2	1,003.0	1,054.2
Gross Unrealized Losses, Less than 12 Months	(74.8)		(244.5)
Gross Unrealized Losses, 12 Months or Greater	(59.8)		(33.3)
Estimated Fair Value	20,666.0		19,254.9
Equity Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	1,316.6		1,195.9
Gross Unrealized Gains	577.1		578.9
Gross Unrealized Losses, Less than 12 Months	(13.7)		(8.0)
Gross Unrealized Losses, 12 Months or Greater	0		0
Estimated Fair Value	1,880.0		1,766.8
Fixed Maturities [Member]
Investments [Line Items]
Cost or Amortized Cost	18,343.8		17,282.6
Gross Unrealized Gains	563.1		475.3
Gross Unrealized Losses, Less than 12 Months	(61.1)		(236.5)
Gross Unrealized Losses, 12 Months or Greater	(59.8)		(33.3)
Estimated Fair Value	18,786.0		17,488.1
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	(5.9)		(0.8)
Fixed Maturities [Member] | United States Government Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	342.6		300.8
Gross Unrealized Gains	3.5		2.5
Gross Unrealized Losses, Less than 12 Months	(0.1)		(3.4)
Gross Unrealized Losses, 12 Months or Greater	(0.2)		0
Estimated Fair Value	345.8		299.9
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	0		0
Fixed Maturities [Member] | Government Sponsored Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	127.1		174.4
Gross Unrealized Gains	0.7		0.4
Gross Unrealized Losses, Less than 12 Months	(0.1)		(1.3)
Gross Unrealized Losses, 12 Months or Greater	(0.7)		0
Estimated Fair Value	127.0		173.5
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	0		0
Fixed Maturities [Member] | States, Municipalities And Political Subdivisions, Tax-Exempt [Member]
Investments [Line Items]
Cost or Amortized Cost	5,725.1		5,899.5
Gross Unrealized Gains	300.2		202.9
Gross Unrealized Losses, Less than 12 Months	(1.5)		(90.1)
Gross Unrealized Losses, 12 Months or Greater	(6.1)		(9.6)
Estimated Fair Value	6,017.7		6,002.7
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	0		(0.6)
Fixed Maturities [Member] | Corporate Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	8,667.5		7,614.1
Gross Unrealized Gains	180.5		205.2
Gross Unrealized Losses, Less than 12 Months	(56.2)		(95.2)
Gross Unrealized Losses, 12 Months or Greater	(34.5)		(15.5)
Estimated Fair Value	8,757.3		7,708.6
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	(5.9)		(0.1)
Fixed Maturities [Member] | Options Embedded In Convertible Debt Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	100.4		89.2
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	100.4		89.2
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	0		0
Fixed Maturities [Member] | Residential Mortgage-Backed Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	2,173.3		2,269.4
Gross Unrealized Gains	62.6		48.0
Gross Unrealized Losses, Less than 12 Months	(2.0)		(41.4)
Gross Unrealized Losses, 12 Months or Greater	(16.4)		(7.1)
Estimated Fair Value	2,217.5		2,268.9
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	0		0
Fixed Maturities [Member] | Commercial Mortgage-Backed Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	502.7		479.0
Gross Unrealized Gains	7.9		10.5
Gross Unrealized Losses, Less than 12 Months	(0.5)		(2.6)
Gross Unrealized Losses, 12 Months or Greater	(0.7)		(0.3)
Estimated Fair Value	509.4		486.6
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	0		0
Fixed Maturities [Member] | Other Debt Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	705.1		456.2
Gross Unrealized Gains	7.7		5.8
Gross Unrealized Losses, Less than 12 Months	(0.7)		(2.5)
Gross Unrealized Losses, 12 Months or Greater	(1.2)		(0.8)
Estimated Fair Value	710.9		458.7
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	$ 0		$ (0.1)