Benefit Plans (Schedule of amounts recognized in Other comprehensive income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax [Abstract]
Amounts arising during the period	$ (31)	$ (29)	$ (111)
Curtailment and other	0	0	56
Settlement	9	(2)	0
Reclassification adjustment relating to prior service credit	(2)	(2)	(3)
Reclassification adjustment relating to actuarial loss	35	37	35
Total increase (decrease) in Other comprehensive income	$ 11	$ 4	$ (23)