Commitments, Contingencies, Guarantees, and Others Commitments, Contingencies, Guarantees, and Others - Schedule of letter of credit and other loan commitments (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Unfunded lending commitments, contractual amount	$ 390,039	$ 382,427
Off-balance sheet lending commitment, carrying value	133	124
Credit Card
Loss Contingencies [Line Items]
Unused commitments to extend credit, contractual amount	352,826	346,186
Other excluding credit card
Loss Contingencies [Line Items]
Unused commitments to extend credit, contractual amount	35,446	34,449
Off-balance sheet lending commitment, carrying value	102	95
Advised line of credit	1,200	1,300
Letter of credit
Loss Contingencies [Line Items]
Standby letters of credit and commercial letters of credit, contractual amount	1,767	1,792
Off-balance sheet lending commitment, carrying value	$ 31	$ 29