Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 1	$ 2
Interest cost	614	731	1,228	1,462
Expected return on plan assets	(939)	(965)	(1,878)	(1,930)
Amortization of prior service credits	(20)	(20)	(40)	(40)
Recognized net actuarial loss	258	160	516	321
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	3		3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(83)	(93)	(170)	(185)
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	20	43	39
Interest cost	36	49	72	98
Expected return on plan assets	(3)	(2)	(5)	(4)
Amortization of prior service credits	(8)	(9)	(17)	(18)
Recognized net actuarial loss	(11)	(12)	(23)	(23)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	36	46	70	92
Operating Income (Loss) | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	1	80	1	158
Operating Income (Loss) | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	23	23	44	45
Other Income | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	(84)	(94)	(171)	(187)
Other Income | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	14	26	27	53
Operating Income (Loss) Before Taxes | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	(83)	(14)	(170)	(29)
Operating Income (Loss) Before Taxes | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	$ 37	$ 49	$ 71	$ 98