Other Postretirement Employee Benefit Plans (Components Of Net Periodic Benefit Cost) (Details) - Other postretirement benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ (1)
Interest cost	(4)	(5)
Amortization of prior service credit	2	2
Amortization of net loss	(1)	0
Total	$ (3)	$ (3)	$ (3)