Employee Benefits - Narrative (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation for all defined benefit pension plans	$ 20,100,000,000	$ 22,200,000,000
Discount Rate	2.90%	2.60%	3.30%	4.40%
Defined benefit plan, reclassification adjustment from AOCI	$ 708,000,000	$ 708,000,000	$ 708,000,000
Defined benefit plan, period used to determine overall expected long term rate of return on assets assumption (in years)	10 years
Number of allocated shares of common stock in ESOP (in shares)	44,000,000
Number of unallocated shares of common stock in ESOP (in shares)	0
Total savings plan cost	$ 690,000,000	730,000,000	897,000,000
Severance, pension and benefit (credits) charges	2,400,000,000	1,600,000,000	126,000,000
Severance costs	209,000,000	221,000,000	204,000,000
Charged to Expense	233,000,000	309,000,000	260,000,000
Changes In Discount Rate Assumption
Defined Benefit Plan Disclosure [Line Items]
Pension and benefit credits (charges)	1,100,000,000	(3,200,000,000)	(4,300,000,000)
Other Assumption Adjustments
Defined Benefit Plan Disclosure [Line Items]
Pension and benefit credits (charges)	(453,000,000)		1,900,000,000
Healthcare Claims and Trend Adjustments
Defined Benefit Plan Disclosure [Line Items]
Pension and benefit credits (charges)			1,600,000,000
Difference Between Estimated Return on Assets and Actual Return On Assets
Defined Benefit Plan Disclosure [Line Items]
Pension and benefit credits (charges)	(847,000,000)	(1,600,000,000)	(2,300,000,000)
Minimum
Defined Benefit Plan Disclosure [Line Items]
Selected bonds	$ 300,000,000
Return Seeking Assets | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets	45.00%
Return Seeking Assets | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets	55.00%
Liability Hedging Assets | Minimum
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets	44.00%
Liability Hedging Assets | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets	54.00%
Cash and cash equivalents | Maximum
Defined Benefit Plan Disclosure [Line Items]
Target allocation percentage of assets	10.00%
Pension
Defined Benefit Plan Disclosure [Line Items]
Pension and benefit credits (charges)	$ 605,000,000	$ (2,308,000,000)
Discount Rate	3.00%	2.60%
Pension and other postretirement benefit obligations	$ 20,167,000,000	$ 22,236,000,000	$ 21,248,000,000
Defined benefit plan contributions by employer	$ 56,000,000	$ 57,000,000
Expected return on plan assets	6.50%	6.50%	6.80%
Pension | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions by employer	$ 0
Pension | Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan contributions by employer	58,000,000
Defined benefit plan contributions by employer in next fiscal year	60,000,000
Health Care and Life
Defined Benefit Plan Disclosure [Line Items]
Pension and benefit credits (charges)	$ 930,000,000	$ (887,000,000)
Discount Rate	2.90%	2.50%
Pension and other postretirement benefit obligations	$ 14,710,000,000	$ 16,168,000,000	$ 15,669,000,000
Defined benefit plan contributions by employer	885,000,000	$ 709,000,000
Defined benefit plan contributions by employer in next fiscal year	$ 860,000,000
Expected return on plan assets	4.20%	4.50%	4.30%
Pension and Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.90%