Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 100	$ 162	$ 301	$ 488
Interest cost	747	761	2,243	2,287
Expected return on plan assets	(961)	(1,000)	(2,883)	(2,998)
Amortization of prior service (credits)/costs	(9)	9	(29)	29
Recognized net actuarial loss	201	198	603	592
Settlement/curtailment/other losses		6	1	39
Net periodic benefit cost	78	136	236	437
Net periodic benefit cost included in Earnings from operations	100	453	534	1,545
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	27	32	80	96
Interest cost	57	66	171	196
Expected return on plan assets	(1)	(2)	(5)	(6)
Amortization of prior service (credits)/costs	(34)	(32)	(102)	(94)
Recognized net actuarial loss	2	5	8	17
Net periodic benefit cost	51	69	152	209
Net periodic benefit cost included in Earnings from operations	$ 58	$ 63	$ 201	$ 213