Available For Sale Securities (Schedule Of Cost And Estimated Fair Values Of Debt Securities By Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Summary Of Significant Accounting Policies [Line Items]
Available-for-sale Securities, Restricted, Total	$ 46.1	$ 0.8
Cost [Member]
Summary Of Significant Accounting Policies [Line Items]
Within one year	33.8
Over one year to five years	8.6	0.8
Over five years to ten years	3.9
Available-for-sale Securities, Restricted, Total	46.3	0.8
Estimated Fair Value [Member]
Summary Of Significant Accounting Policies [Line Items]
Within one year	33.7
Over one year to five years	8.6	0.8
Over five years to ten years	3.8
Available-for-sale Securities, Restricted, Total	$ 46.1	$ 0.8