Investments (Rollforward Of Cumulative Amounts Related To Credit Loss Portion Of OTTI Losses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Investments [Abstract]
Credit losses as of the beginning of the period	$ 14.5	$ 16.7
Credit losses for which an OTTI was not previously recognized	0.1
Additional credit losses on securities for which an OTTI was previously recognized	0.3	0.2
Reductions for securities sold, matured or called during the period	(1.4)	(0.6)
Credit losses as of the end of the period	$ 13.5	$ 16.3