Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Jan. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Summary of Accounting and Financial Policies [Line Items]
Cash and due from banks		$ 14,270		$ 11,150
Interest-bearing deposits with banks		108,770		110,560
Cash segregated for regulatory and other purposes		15,180		14,650
Loans held for sale		2,910		2,600
Impact of adoption of accounting standard ASU No. 2016-18			$ 448
Accounting Standards Update 2015-02 [Member]
Summary of Accounting and Financial Policies [Line Items]
Impact of adoption of accounting standard ASU No. 2015-02	$ 200
Accounting Standards Update 2016-09 [Member]
Summary of Accounting and Financial Policies [Line Items]
Reduction to the provision for taxes from the impact of the RSU deliveries and option exercises in 1Q 2017		(475)
New accounting standards impact on share based award		35
New accounting standards impact on retained earnings		(24)
New accounting standards impact on deferred income taxes		11
New accounting standard adoption impact on cash flows from financing activities		888
Impact of adoption of accounting standard ASU No. 2016-18		$ 54
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