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	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 407.7	$ 255.6	$ 315.8	$ 202.8
Total gains (losses) recognized in net income	(0.5)	0.3	0.1	(1.7)
Total gains (losses) recognized in accumulated other comprehensive loss	(0.6)	3.7	(2.6)	7.4
Purchases	69.7	20.1	233.9	125.2
Sales	(11.4)	(15.3)	(23.7)	(26.0)
Settlements	(6.6)	(2.8)	(27.8)	(28.3)
Transfers into Level III	13.8	0.0	35.5	4.9
Transfers out of Level III	0.0	(14.0)	(59.1)	(36.7)
Ending balance	472.1	247.6	472.1	247.6
Change in unrealized losses included in net income related to assets still held	(0.1)	0.0	(1.9)	(1.6)
Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	208.1	192.4	186.2	144.6
Total gains (losses) recognized in net income	0.0	0.3	(1.6)	(0.7)
Total gains (losses) recognized in accumulated other comprehensive loss	0.2	0.3	(1.1)	3.3
Purchases	46.7	10.1	138.6	99.7
Sales	(3.3)	(6.1)	(5.1)	(10.2)
Settlements	(6.0)	(2.1)	(27.2)	(27.0)
Transfers into Level III	2.2	0.0	5.1	4.9
Transfers out of Level III	0.0	(8.8)	(47.0)	(28.5)
Ending balance	247.9	186.1	247.9	186.1
Change in unrealized losses included in net income related to assets still held	(0.1)	0.0	(1.9)	(0.6)
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1.6	0.0	0.0	0.0
Total gains (losses) recognized in net income	0.0	0.0	0.0	0.0
Total gains (losses) recognized in accumulated other comprehensive loss	0.0	0.0	0.0	0.0
Purchases	3.6	0.0	3.6	0.0
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Transfers into Level III	0.0	0.0	1.6	0.0
Transfers out of Level III	0.0	0.0	0.0	0.0
Ending balance	5.2	0.0	5.2	0.0
Change in unrealized losses included in net income related to assets still held	0.0	0.0	0.0	0.0
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0.0	2.8	1.9	3.3
Total gains (losses) recognized in net income	0.0	0.0	0.0	0.0
Total gains (losses) recognized in accumulated other comprehensive loss	0.0	0.0	0.0	0.0
Purchases	0.0	1.1	0.0	1.1
Sales	0.0	(1.1)	0.0	(1.1)
Settlements	0.0	(0.6)	0.0	(1.1)
Transfers into Level III	0.0	0.0	0.0	0.0
Transfers out of Level III	0.0	0.0	(1.9)	0.0
Ending balance	0.0	2.2	0.0	2.2
Change in unrealized losses included in net income related to assets still held	0.0	0.0	0.0	0.0
Other Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	32.3	6.3	25.6	6.6
Total gains (losses) recognized in net income	0.0	0.0	0.0	0.2
Total gains (losses) recognized in accumulated other comprehensive loss	(0.1)	0.0	(0.4)	(0.2)
Purchases	0.0	0.0	0.0	3.7
Sales	0.0	0.0	0.0	(0.9)
Settlements	(0.5)	(0.1)	(0.5)	(0.2)
Transfers into Level III	11.6	0.0	28.8	0.0
Transfers out of Level III	0.0	(5.2)	(10.2)	(8.2)
Ending balance	43.3	1.0	43.3	1.0
Change in unrealized losses included in net income related to assets still held	0.0	0.0	0.0	0.0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	165.7	54.1	102.1	48.3
Total gains (losses) recognized in net income	(0.5)	0.0	1.7	(1.2)
Total gains (losses) recognized in accumulated other comprehensive loss	(0.7)	3.4	(1.1)	4.3
Purchases	19.4	8.9	91.7	20.7
Sales	(8.1)	(8.1)	(18.6)	(13.8)
Settlements	(0.1)	0.0	(0.1)	0.0
Transfers into Level III	0.0	0.0	0.0	0.0
Transfers out of Level III	0.0	0.0	0.0	0.0
Ending balance	175.7	58.3	175.7	58.3
Change in unrealized losses included in net income related to assets still held	$ 0.0	$ 0.0	$ 0.0	$ (1.0)