Commitments, Contingencies, Guarantees, and Others Commitments, Contingencies, Guarantees, and Others - Schedule of letter of credit and other loan commitments (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Letter of Credit Issued Contractual Amount and Unused Commitment to Extend Credit	$ 382,427	$ 385,367
Off-balance Sheet Lending Commitment Carrying Value	124	127
Credit Card Portfolio Segment
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	346,186	351,481
Other Portfolio Segments, Excluding Credit Card
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	34,449	31,840
Off-balance Sheet Lending Commitment Carrying Value	95	84
Advised Line of Credit	1,300	1,000
Letter of Credit [Member]
Loss Contingencies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,792	2,046
Off-balance Sheet Lending Commitment Carrying Value	$ 29	$ 43