Investments (Schedule Of Gross Unrealized Losses And Fair Value Of Investments) (Details) (Corporate Bonds [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012 NumberOfInvestments	Dec. 31, 2011 NumberOfInvestments
Corporate Bonds [Member]
Unrealized losses, Number	98	360
Unrealized losses	$ 2.8	$ 20.9
Unrealized losses, Less than 12 months, Number	82	334
Unrealized losses, Less than 12 months	1.6	17.4
Unrealized losses, 12 or more months, Number	16	26
Unrealized losses, 12 or more months	1.2	3.5
Fair market value of securities with unrealized losses, Number	98	360
Fair market value of securities with unrealized losses, Amount	87.0	425.3
Fair market value of securities with unrealized losses, Less than 12 months, Number	82	334
Fair market value of securities with unrealized losses, Less than 12 months, Amount	71.4	398.0
Fair market value of securities with unrealized losses, 12 or more months, Number	16	26
Fair market value of securities with unrealized losses, 12 or more months, Amount	$ 15.6	$ 27.3