Employee Benefits - Additional Information (Detail) - USD ($)	3 Months Ended					9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Amount paid in severance benefits over the period						$ 169,000,000
Pre-tax severance charges	$ 109,000,000					124,000,000
Charges related to voluntary separations	103,000,000					103,000,000
Post employment benefits liability	529,000,000					529,000,000
Pension
Defined Benefit Plan Disclosure [Line Items]
Remeasurement gain (loss), net	(144,000,000)	$ 1,300,000,000	$ (1,092,000,000)	$ (153,000,000)	$ (182,000,000)	1,170,000,000	$ (1,427,000,000)
Charge (credit) due to change in discount rate assumption	667,000,000	1,200,000,000	1,800,000,000		$ (196,000,000)
Credit (charge) due to difference between estimated and actual return on assets	523,000,000	$ 122,000,000	689,000,000	$ (163,000,000)
Pension | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Employer discretionary contribution amount	$ 0		$ 0			$ 0	$ 0