Derivative Financial Instruments (Effect Of Cash Flow Hedges On Financial Statements) (Details) - Forward Starting Pay Fixed Swaps [Member] - Cash Flow Hedging [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Gain (Loss) Recognized In Other Comprehensive Income (Loss)	$ 0	$ (35)	$ (33)
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedge (loss) gain reclassified from accumulated other comprehensive loss	$ (15)	$ (15)	$ (14)