Leases - Narrative (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 5,852
Weighted average lease term	7 years 6 months
Weighted average discount rate used to measure lease liabilities	3.90%
Other Assets [Member]
Lessee, Lease, Description [Line Items]
Operating leases, right of use assets	$ 5,996
Accounts Payable, Accruals and Other Liabilities [Member]
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 5,852