Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 107	$ 2	$ 215
Interest cost	731	695	1,462	1,390
Expected return on plan assets	(965)	(1,003)	(1,930)	(2,005)
Amortization of prior service credits	(20)	(14)	(40)	(28)
Recognized net actuarial loss	160	283	321	565
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment		(43)		(43)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(93)	111	(185)	180
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	20	23	39	47
Interest cost	49	48	98	97
Expected return on plan assets	(2)	(2)	(4)	(4)
Amortization of prior service credits	(9)	(31)	(18)	(63)
Recognized net actuarial loss	(12)	(2)	(23)	(5)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	46	36	92	72
Operating Income (Loss) [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	80	76	158	158
Operating Income (Loss) [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	23	20	45	42
Other Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	(94)	(6)	(187)	(48)
Other Income [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	26	24	53	48
Operating Income (Loss) Before Taxes [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost included in Earnings from operations	(14)	70	(29)	110
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	$ 49	$ 44	$ 98	$ 90