Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 107	$ 100	$ 215	$ 201
Interest cost	695	748	1,390	1,496
Expected return on plan assets	(1,003)	(961)	(2,005)	(1,922)
Amortization of prior service credits	(14)	(10)	(28)	(20)
Recognized net actuarial loss	283	201	565	402
Settlement/curtailment/other losses	43		43	1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	111	78	180	158
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	23	27	47	53
Interest cost	48	57	97	114
Expected return on plan assets	(2)	(2)	(4)	(4)
Amortization of prior service credits	(31)	(34)	(63)	(68)
Recognized net actuarial loss	(2)	3	(5)	6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	36	51	72	101
Operating Income (Loss) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	76	122	158	253
Operating Income (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	20	25	42	53
Other Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	(6)	(28)	(48)	(62)
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	48	60
Operating Income (Loss) Before Taxes [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	70	94	110	191
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	$ 44	$ 55	$ 90	$ 113