Asset-Backed Financing (Schedule Of Secured Notes With Related Maturity) (Details) - Variable Interest Entity, Primary Beneficiary - Secured Debt - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Weighted average interest rate at date of issuance	1.53%	1.31%
Secured Notes Issued May 2015
Debt Instrument [Line Items]
Company issued secured notes	$ 500,000,000
Weighted average interest rate at date of issuance	0.88%
Secured Notes Issued January 2015
Debt Instrument [Line Items]
Company issued secured notes	$ 700,000,000
Weighted average interest rate at date of issuance	0.89%
Secured Notes Issued April 2014
Debt Instrument [Line Items]
Company issued secured notes	$ 850,000,000
Weighted average interest rate at date of issuance	0.66%
Secured Notes Issued April 2013
Debt Instrument [Line Items]
Company issued secured notes	$ 650,000,000
Weighted average interest rate at date of issuance	0.57%