Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 108	$ 101
Interest cost	695	748
Expected return on plan assets	(1,002)	(961)
Amortization of prior service credits	(14)	(10)
Recognized net actuarial loss/(gain)	282	201
Settlement/curtailment/other losses		1
Net periodic benefit cost	69	80
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	24	26
Interest cost	49	57
Expected return on plan assets	(2)	(2)
Amortization of prior service credits	(32)	(34)
Recognized net actuarial loss/(gain)	(3)	3
Settlement/curtailment/other losses
Net periodic benefit cost	36	50
Operating Income (Loss) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	82	131
Operating Income (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	22	28
Other Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	(42)	(34)
Other Income [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	24	30
Operating Income (Loss) Before Taxes [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	40	97
Operating Income (Loss) Before Taxes [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	$ 46	$ 58