Leases and Lease Commitments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Leased Assets [Line Items]
Total rental expense	$ 1,400	$ 1,700	$ 1,700
Operating lease, asset	$ 800	$ 1,300
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsMember	us-gaap:OtherAssetsMember
Operating lease, liability	$ 1,011	$ 1,000
Operating lease, weighted average remaining lease term	8 years
Operating lease, weighted average discount rate, percent	3.20%
Accounts Payable and Accrued Liabilities
Operating Leased Assets [Line Items]
Operating lease, liability	$ 248	200
Other Liabilities
Operating Leased Assets [Line Items]
Operating lease, liability	$ 763	$ 800