Fair Value (Reconciliation Of The Beginning And Ending Balances Of Assets Measured At Fair Value On A Recurring Basis Using Level III Inputs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 193.0	$ 167.1	$ 155.5	$ 284.8
Total gains (losses) recognized in net income	(15.0)	(0.4)	(17.1)	14.9
Total gains (losses) recognized in accumulated other comprehensive income	2.6	(2.8)	7.0	(27.8)
Purchases	10.1	19.8	56.5	69.7
Sales	(1.6)	(21.2)	(4.1)	(33.3)
Issuances	0	0	0	0
Settlements	(5.2)	(6.0)	(17.4)	(65.6)
Transfers into Level III	25.4	10.0	38.5	29.5
Transfers out of Level III	(12.9)	(5.8)	(22.5)	(111.5)
Ending balance	196.4	160.7	196.4	160.7
Change in unrealized losses included in net income related to assets still held	(15.0)	(0.2)	(19.6)	(0.6)
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	139.2	127.7	121.1	195.1
Total gains (losses) recognized in net income	(14.9)	(0.2)	(16.0)	15.3
Total gains (losses) recognized in accumulated other comprehensive income	4.9	2.0	1.8	(15.5)
Purchases	6.4	15.6	45.3	61.8
Sales	(1.6)	(21.2)	(1.6)	(26.3)
Issuances	0	0	0	0
Settlements	(2.7)	(5.7)	(12.6)	(64.5)
Transfers into Level III	3.0	0	3.0	1.7
Transfers out of Level III	0	(5.8)	(6.7)	(55.2)
Ending balance	134.3	112.4	134.3	112.4
Change in unrealized losses included in net income related to assets still held	(14.9)	0	(16.5)	0
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	12.6	1.4	4.3	0
Total gains (losses) recognized in net income	0	0	0	0
Total gains (losses) recognized in accumulated other comprehensive income	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	(1.9)	0
Transfers into Level III	0	0	13.1	1.4
Transfers out of Level III	(12.6)	0	(15.5)	0
Ending balance	0	1.4	0	1.4
Change in unrealized losses included in net income related to assets still held	0	0	0	0
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	5.3	0	6.3
Total gains (losses) recognized in net income	0	0	0	0
Total gains (losses) recognized in accumulated other comprehensive income	0	0.1	0	0.1
Purchases	0	0	0	3.4
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(2.3)	(0.1)	(2.3)	(0.1)
Transfers into Level III	12.6	0	12.6	1.9
Transfers out of Level III	0	0	0	(6.3)
Ending balance	10.3	5.3	10.3	5.3
Change in unrealized losses included in net income related to assets still held	0	0	0	0
Other Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	5.4	3.9	3.9	59.0
Total gains (losses) recognized in net income	(0.1)	0	(0.1)	0.1
Total gains (losses) recognized in accumulated other comprehensive income	0.1	0.6	0.4	0.8
Purchases	0	0	1.6	0
Sales	0	0	0	(6.6)
Issuances	0	0	0	0
Settlements	(0.2)	(0.2)	(0.6)	(1.0)
Transfers into Level III	9.8	10.0	9.8	12.0
Transfers out of Level III	(0.3)	0	(0.3)	(50.0)
Ending balance	14.7	14.3	14.7	14.3
Change in unrealized losses included in net income related to assets still held	(0.1)	0	(0.1)	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	35.8	28.8	26.2	24.4
Total gains (losses) recognized in net income	0	(0.2)	(1.0)	(0.5)
Total gains (losses) recognized in accumulated other comprehensive income	(2.4)	(5.5)	4.8	(13.2)
Purchases	3.7	4.2	9.6	4.5
Sales	0	0	(2.5)	(0.4)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level III	0	0	0	12.5
Transfers out of Level III	0	0	0	0
Ending balance	37.1	27.3	37.1	27.3
Change in unrealized losses included in net income related to assets still held	$ 0	$ (0.2)	$ (3.0)	$ (0.6)