Postretirement Plans (Net Periodic Benefit Cost Tables) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 2	$ 1
Interest cost	497	614	995	1,228
Expected return on plan assets	(965)	(939)	(1,931)	(1,878)
Amortization of prior service credits	(20)	(20)	(40)	(40)
Recognized net actuarial loss	310	258	620	516
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	3	3	4	3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(174)	(83)	(350)	(170)
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	22	44	43
Interest cost	22	36	45	72
Expected return on plan assets	(1)	(3)	(3)	(5)
Amortization of prior service credits	(8)	(8)	(17)	(17)
Recognized net actuarial loss	(18)	(11)	(35)	(23)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	17	36	34	70
Operating Income (Loss) | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	1	1	2	1
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	22	23	44	44
Other Income | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	(175)	(84)	(352)	(171)
Other Income | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (Loss)/earnings before income taxes	(5)	14	(10)	27
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	(174)	(83)	(350)	(170)
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	$ 17	$ 37	$ 34	$ 71