Benefit Plans (Schedule of amounts recognized in Other comprehensive income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, [Abstract]
Amounts arising during the period	$ (29)	$ (111)	$ (337)
Curtailment and other	0	56	(81)
Settlement through group annuity purchase	0	0	84
Reclassification adjustment relating to prior service cost (credit)	(2)	(3)	(10)
Reclassification adjustment relating to actuarial (gain) loss	37	35	26
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Settlements Through Group Annuity Purchase, before Tax	(2)	0	0
Total increase (decrease) in Other comprehensive income	$ 4	$ (23)	$ (318)