Leases - Narrative (Detail) $ in Millions	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 6,010
Weighted average lease term	7 years 8 months 12 days
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	$ 6,200
Accounts Payable, Accruals and Other Liabilities [Member]
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 6,000