Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1		$ 2	$ 2
Interest cost	613	731	1,841	2,193
Expected return on plan assets	(938)	(966)	(2,816)	(2,896)
Amortization of prior service credits	(20)	(19)	(60)	(59)
Recognized net actuarial loss	258	161	774	482
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	3		6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(83)	(93)	(253)	(278)
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	3,000		3,000
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	19	65	58
Interest cost	35	49	107	147
Expected return on plan assets	(1)	(2)	(6)	(6)
Amortization of prior service credits	(12)	(8)	(29)	(26)
Recognized net actuarial loss	(10)	(12)	(33)	(35)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	(2)		(2)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	32	46	102	138
Operating Income (Loss) | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	1	76	2	234
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	21	67	66
Other Income | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	(84)	(93)	(255)	(280)
Other Income | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	10	27	37	80
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)	(17)	(253)	(46)
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	$ 33	$ 48	$ 104	$ 146