Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 107	$ 2	$ 322
Interest cost	731	696	2,193	2,086
Expected return on plan assets	(966)	(1,002)	(2,896)	(3,007)
Amortization of prior service credits	(19)	(14)	(59)	(42)
Recognized net actuarial loss	161	282	482	847
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment				(43)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(93)	69	(278)	249
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	19	24	58	71
Interest cost	49	48	147	145
Expected return on plan assets	(2)	(2)	(6)	(6)
Amortization of prior service credits	(8)	(31)	(26)	(94)
Recognized net actuarial loss	(12)	(3)	(35)	(8)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	46	36	138	108
Operating Income (Loss) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	76	79	234	237
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	21	66	63
Other Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	(93)	(50)	(280)	(98)
Other Income [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	27	29	80	77
Operating Income (Loss) Before Taxes [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	(17)	29	(46)	139
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	$ 48	$ 50	$ 146	$ 140