Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Summary of Investments in Community Development and Tax-advantaged VIEs (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Investment carrying amount	$ 546,652	$ 495,426
Unfunded capital and other commitments	494,172	442,943
Variable Interest Entity Not Primary Beneficiary [Member] | Community Development And Tax Advantaged Investments [Member]
Variable Interest Entity [Line Items]
Investment carrying amount	6,345	6,148
Unfunded capital and other commitments	2,966	2,938
Maximum exposure to loss	$ 12,204	$ 12,118