Long-Term Debt (Schedule Of Senior Medium-Term Notes) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt, interest rate 4.5%	4.50%
Senior medium-term notes	$ 1,147	$ 637
Senior Medium Term Notes, Par Amount	$ 1,136
Long-term debt, interest rate 3.5%	3.50%
Long-term debt, interest rate 3.35%	3.35%
Senior Medium-Term Notes four point five zero percent with maturity of June 2023 [Member]
Debt Instrument [Line Items]
Senior medium-term notes	$ 131
Senior Medium Term Notes, Par Amount	136
Senior medium-term notes, interest rate, 3.50 [Member]
Debt Instrument [Line Items]
Senior medium-term notes	509
Senior Medium Term Notes, Par Amount	500
Senior medium-term notes, interest rate, 3.35 [Member]
Debt Instrument [Line Items]
Senior medium-term notes	507
Senior Medium Term Notes, Par Amount	$ 500