Postretirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 32	$ 35	$ 96	$ 105
Interest cost	66	62	196	186
Expected return on plan assets	(2)	(2)	(6)	(6)
Amortization of prior service costs	(32)	(34)	(94)	(102)
Recognized net actuarial loss	5	8	17	23
Settlement/curtailment/other losses		4		9
Net periodic benefit cost	69	73	209	215
Net periodic benefit cost included in Earnings from operations	63	65	213	226
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	162	441	488	1,325
Interest cost	761	748	2,287	2,242
Expected return on plan assets	(1,000)	(1,008)	(2,998)	(3,024)
Amortization of prior service costs	9	49	29	147
Recognized net actuarial loss	198	392	592	1,184
Settlement/curtailment/other losses	6	83	39	194
Net periodic benefit cost	136	705	437	2,068
Net periodic benefit cost included in Earnings from operations	$ 453	$ 529	$ 1,545	$ 1,837