Leases - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating leases, right of use assets		$ 5,579	$ 5,941
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssets	us-gaap:OtherAssets
Operating lease liabilities		$ 5,469	$ 5,882
Operating Lease, Liability, Statement of Financial Position [Extensible List]		us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
Weighted average lease term		7 years 3 months 18 days	7 years 8 months 12 days
Weighted average discount rate used to measure lease liabilities		3.60%	3.80%
Operating lease expense	$ 1,649