Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Summary of Accounting and Financial Policies [Line Items]
Cash and due from banks		$ 6,850	$ 6,470
Interest-bearing deposits with banks		92,690	68,640
Loans held for sale		3,120	$ 2,350
Impact of adoption of accounting standards		200
Accumulated Other Comprehensive Loss [Member] | Accounting Standards Update 2016-01 [Member]
Summary of Accounting and Financial Policies [Line Items]
Reclassification of cumulative debt valuation adjustment, net of tax, from retained earnings to accumulated other comprehensive loss	$ 305	$ 305