Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 107	$ 100	$ 322	$ 301
Interest cost	696	747	2,086	2,243
Expected return on plan assets	(1,002)	(961)	(3,007)	(2,883)
Amortization of prior service credits	(14)	(9)	(42)	(29)
Recognized net actuarial loss	282	201	847	603
Settlement/curtailment/other losses			43	1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	69	78	249	236
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	24	27	71	80
Interest cost	48	57	145	171
Expected return on plan assets	(2)	(1)	(6)	(5)
Amortization of prior service credits	(31)	(34)	(94)	(102)
Recognized net actuarial loss	(3)	2	(8)	8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	36	51	108	152
Operating Income (Loss) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	79	123	237	376
Operating Income (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	21	25	63	78
Other Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	(50)	(26)	(98)	(88)
Other Income [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	29	31	77	91
Operating Income (Loss) Before Taxes [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	29	97	139	288
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	$ 50	$ 56	$ 140	$ 169