Common Stock And Share-Based Compensation (Restricted Stock Units) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock And Share-Based Compensation [Abstract]
Total fair value	$ 57	$ 36	$ 57
Total unrecognized compensation costs	$ 33
Remaining weighted average period, Years	1 year 5 months 16 days
Nonvested at January 1, Number of Restricted Stock Units	1,923,010
Granted, Number of Restricted Stock Units	658,395
Vested, Number of Restricted Stock Units	(1,172,194)
Forfeited, Number of Restricted Stock Units	(29,976)
Nonvested at December 31, Number of Restricted Stock Units	1,379,235	1,923,010
Nonvested at January 1, Weighted Average Grant-Date Fair Value	$ 51.26
Granted, Weighted Average Grant Date Fair Value	66.95	$ 56.68	$ 53.30
Vested, Weighted Average Grant Date Fair Value	48.44
Forfeited, Weighted Average Grant Date Fair Value	61.07
Nonvested at December 31, Weighted Average Grant-Date Fair Value	$ 60.93	$ 51.26