Postretirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 163	$ 442
Interest cost	764	747
Expected return on plan assets	(999)	(1,008)
Amortization of prior service costs	10	49
Recognized net actuarial loss	197	396
Settlement/curtailment/other losses	15	38
Net periodic benefit cost	150	664
Net periodic benefit cost included in Earnings from operations	629	785
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	32	35
Interest cost	65	62
Expected return on plan assets	(2)	(2)
Amortization of prior service costs	(31)	(34)
Recognized net actuarial loss	$ 6	4
Settlement/curtailment/other losses		2
Net periodic benefit cost	$ 70	67
Net periodic benefit cost included in Earnings from operations	$ 88	$ 92