Benefit Plans (Schedule of amounts recognized in Other comprehensive income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, [Abstract]
Amounts arising during the period	$ (111)	$ (337)	$ 422
Curtailment and other	56	(81)	0
Settlement	0	84	0
Reclassification adjustment relating to prior service cost (credit)	(3)	(10)	(18)
Reclassification adjustment relating to actuarial (gain) loss	35	26	49
Total increase (decrease) in Other comprehensive income	$ (23)	$ (318)	$ 453