Nature Of Operations And Significant Accounting Policies (Summary Of Allowance For Doubtful Accounts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	$ 7.3	$ 4.7	$ 4.9
Provision for Loan, Lease, and Other Losses	2.2	6.1	3.0
Financing Receivable, Allowance for Credit Losses, Write-downs	(2.3)	(3.5)	(3.2)
Balance at end of year	$ 7.2	$ 7.3	$ 4.7