Accounting for Transfers and Servicing of Financial Assets and Variable Interest Entities - Summary of Investments in Community Development and Tax-advantaged VIEs (Detail) - Community Development and Tax Advantaged Investments [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Investment carrying amount	$ 5,517	$ 5,660
Unfunded capital and other commitments	2,583	2,770
Maximum exposure to loss	$ 12,173	$ 12,120