Investment Income And Gains And Losses (Reconciliation Of Gross Unrealized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investment Income And Gains And Losses [Abstract]
Unrealized gains arising during period, Pre-Tax	$ 97.8	$ 130.7	$ 413.6
Unrealized gains arising during period, Tax Benefit (Expense)	(23.5)	(9.1)	1.3
Unrealized gains arising during period, Net of Tax	121.3	139.8	414.9
Less: reclassification adjustments for gains realized in net income, Pre-Tax	20.4	26.0	(2.2)
Less: reclassification adjustments for gains realized in net income, Tax Benefit (Expense)	9.3	3.2
Less: reclassification adjustments for gains realized in net income, Net of Tax	29.7	29.2	(2.2)
Total available-for-sale securities, Pre-Tax	77.4	104.7	415.8
Total available-for-sale securities, Tax Benefit (Expense)	14.2	5.9	1.3
Total available-for-sale securities	91.6	110.6	417.1
Unrealized losses arising during period, Pre-Tax	(1.8)
Unrealized losses arising during period, Tax Benefit (Expense)	0.6
Unrealized losses arising during period, Net of Tax	(1.2)
Other comprehensive income, Pre-Tax	75.6	104.7	415.8
Other comprehensive income, Tax Benefit (Expense)	14.8	5.9	1.3
Other comprehensive income, Net of Tax	$ 90.4	$ 110.6	$ 417.1