Long-Term Debt (Schedule Of Mandatory Debt Payments) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Long-Term Debt [Abstract]
Debt Maturity, Mandatory Repayment, In Two Years	$ 500,000,000
Debt Maturity, Mandatory Repayment, In Four Years	600,000,000
Debt Maturity, Mandatory Repayment, After Five Years	3,111,000,000
Total Principal	4,211,000,000	$ 4,211,000,000
Interest Payments on Remaining Long-term Debt, Next Twelve Months	267,000,000
Interest Payments on Remaining Long-term Debt in Year two	251,000,000
Interest Payments on Remaining Long-term Debt in Year Three	234,000,000
Interest Payments on Remaining Long-term Debt in Year Four	235,000,000
Interest Payments on Remaining Long-term Debt in Year Five	211,000,000
Interest Payments on Remaining Long-term Debt, After Five Years	2,546,000,000
Total Interest Payments on Remaining Long-term Debt	$ 3,744,000,000