Summary Of Significant Accounting Policies (Schedule Of Other Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Other Income	$ 57.4	$ 51.9	$ 46.6
Ancillary Product Profit Sharing [Member]
Summary Of Significant Accounting Policies [Line Items]
Other Income	23.9	15.5	11.9
GPS-SID Fees [Member]
Summary Of Significant Accounting Policies [Line Items]
Other Income	11.1	13.5	16.4
Remarketing Fees [Member]
Summary Of Significant Accounting Policies [Line Items]
Other Income	10.9	9.2	6.9
Dealer Enrollment Fees [Member]
Summary Of Significant Accounting Policies [Line Items]
Other Income	3.9	5.0	4.8
Dealer Support Products And Services [Member]
Summary Of Significant Accounting Policies [Line Items]
Other Income	4.8	4.7	4.9
Other [Member]
Summary Of Significant Accounting Policies [Line Items]
Other Income	$ 2.8	$ 4.0	$ 1.7