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, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
off-balance sheet lending commitment carrying value	$ 140	$ 171
Letter of credit issued contractual amount and unused commitment to extend credit	343,202	338,014
Letter of Credit [Member]
Loss Contingencies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,936	1,874
off-balance sheet lending commitment carrying value	42	37
Credit Card Portfolio Segment [Member]
Loss Contingencies [Line Items]
Unused Commitments to Extend Credit	312,864	308,257
Other Portfolio Segments, Excluding Credit Card
Loss Contingencies [Line Items]
Advised Line of Credit	699	1,000
off-balance sheet lending commitment carrying value	98	134
Unused Commitments to Extend Credit	$ 28,402	$ 27,883