Investments (Current And Long-Term Investments, Available-For-Sale) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Investments [Line Items]
Cost or Amortized Cost	$ 19,535.4		$ 18,478.5
Gross Unrealized Gains	1,284.8	1,016.4	1,054.2
Gross Unrealized Losses, Less than 12 Months	(13.3)		(244.5)
Gross Unrealized Losses, 12 Months or Greater	(51.7)		(33.3)
Estimated Fair Value	20,755.2		19,254.9
Equity Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	1,295.4		1,195.9
Gross Unrealized Gains	628.2		578.9
Gross Unrealized Losses, Less than 12 Months	(4.5)		(8.0)
Gross Unrealized Losses, 12 Months or Greater	0		0
Estimated Fair Value	1,919.1		1,766.8
Fixed Maturities [Member]
Investments [Line Items]
Cost or Amortized Cost	18,240.0		17,282.6
Gross Unrealized Gains	656.6		475.3
Gross Unrealized Losses, Less than 12 Months	(8.8)		(236.5)
Gross Unrealized Losses, 12 Months or Greater	(51.7)		(33.3)
Estimated Fair Value	18,836.1		17,488.1
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	(0.8)		(0.8)
Fixed Maturities [Member] | United States Government Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	509.3		300.8
Gross Unrealized Gains	5.2		2.5
Gross Unrealized Losses, Less than 12 Months	0		(3.4)
Gross Unrealized Losses, 12 Months or Greater	(0.3)		0
Estimated Fair Value	514.2		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	148.1		174.4
Gross Unrealized Gains	0.9		0.4
Gross Unrealized Losses, Less than 12 Months	0		(1.3)
Gross Unrealized Losses, 12 Months or Greater	(0.7)		0
Estimated Fair Value	148.3		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	5,704.5		5,899.5
Gross Unrealized Gains	280.9		202.9
Gross Unrealized Losses, Less than 12 Months	(1.1)		(90.1)
Gross Unrealized Losses, 12 Months or Greater	(13.0)		(9.6)
Estimated Fair Value	5,971.3		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	8,497.8		7,614.1
Gross Unrealized Gains	280.7		205.2
Gross Unrealized Losses, Less than 12 Months	(6.2)		(95.2)
Gross Unrealized Losses, 12 Months or Greater	(20.4)		(15.5)
Estimated Fair Value	8,751.9		7,708.6
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	(0.8)		(0.1)
Fixed Maturities [Member] | Options Embedded In Convertible Debt Securities [Member]
Investments [Line Items]
Cost or Amortized Cost	103.5		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	103.5		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	2,178.2		2,269.4
Gross Unrealized Gains	69.8		48.0
Gross Unrealized Losses, Less than 12 Months	(1.2)		(41.4)
Gross Unrealized Losses, 12 Months or Greater	(15.2)		(7.1)
Estimated Fair Value	2,231.6		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	509.9		479.0
Gross Unrealized Gains	10.8		10.5
Gross Unrealized Losses, Less than 12 Months	(0.1)		(2.6)
Gross Unrealized Losses, 12 Months or Greater	(0.6)		(0.3)
Estimated Fair Value	520.0		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	588.7		456.2
Gross Unrealized Gains	8.3		5.8
Gross Unrealized Losses, Less than 12 Months	(0.2)		(2.5)
Gross Unrealized Losses, 12 Months or Greater	(1.5)		(0.8)
Estimated Fair Value	595.3		458.7
Non-credit component of other-than-temporary impairments recognized in accumulated other comprehensive income	$ 0		$ (0.1)