Postretirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 26	$ 32
Interest cost	57	65
Expected return on plan assets	(2)	(2)
Amortization of prior service (credits)/costs	(34)	(31)
Recognized net actuarial loss	3	6
Settlement/curtailment/other losses
Net periodic benefit cost	50	70
Net periodic benefit cost included in Earnings from operations	85	88
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	101	163
Interest cost	748	764
Expected return on plan assets	(961)	(999)
Amortization of prior service (credits)/costs	(10)	10
Recognized net actuarial loss	201	197
Settlement/curtailment/other losses	1	15
Net periodic benefit cost	80	150
Net periodic benefit cost included in Earnings from operations	$ 334	$ 629