Share-Based Compensation (Schedule Of Aggregate Fair Value Of Restricted Stock, Performance-Based Restricted Stock And Performance Shares, Awards And Units, That Vested During The Period) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Awards And Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate fair value of awards and units, vested	$ 105	$ 73	$ 101
Performance-Based Restricted Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate fair value of awards and units, vested	10	5	8
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate fair value of awards and units, vested	$ 38	$ 13	$ 22