Derivatives and Hedging Activities - Fair Value of Derivatives by Level (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Total financial assets at fair value	$ 539,568	$ 501,712
Total financial liabilities at fair value	(332,959)	(296,504)
Fair value included in financial instruments	(108,835)	(108,897)
Level 1 [Member]
Derivative [Line Items]
Total financial assets at fair value	242,562	170,463
Total financial liabilities at fair value	(54,790)	(54,151)
Level 2 [Member]
Derivative [Line Items]
Total financial assets at fair value	325,259	354,515
Total financial liabilities at fair value	(293,902)	(258,335)
Level 3 [Member]
Derivative [Line Items]
Total financial assets at fair value	23,068	22,181
Total financial liabilities at fair value	(25,938)	(23,804)
Derivatives [Member]
Derivative [Line Items]
Total financial assets at fair value	100,779	94,229
Total financial liabilities at fair value	(85,473)	(82,380)
Fair value included in financial instruments	45,252	44,846
Fair value included in financial instruments	(43,802)	(42,594)
Derivatives [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	280,003	236,100
Total financial liabilities at fair value	(251,521)	(216,203)
Derivatives [Member] | Credit Risk Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	20,729	19,436
Total financial liabilities at fair value	(20,789)	(18,301)
Derivatives [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	80,365	86,518
Total financial liabilities at fair value	(82,224)	(88,883)
Derivatives [Member] | Commodity Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	11,138	17,624
Total financial liabilities at fair value	(15,549)	(20,127)
Derivatives [Member] | Equity Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	49,661	48,118
Total financial liabilities at fair value	(56,507)	(52,433)
Derivatives [Member] | Gross Fair Value Of Derivative [Member]
Derivative [Line Items]
Total financial assets at fair value	441,896	407,796
Total financial liabilities at fair value	(426,590)	(395,947)
Derivatives [Member] | Counterparty Netting in Levels [Member]
Derivative [Line Items]
Total financial assets at fair value	(341,117)	(313,567)
Total financial liabilities at fair value	341,117	313,567
Derivatives [Member] | Cross Level Counterparty Netting Adjustment [Member]
Derivative [Line Items]
Total financial assets at fair value	473	(659)
Total financial liabilities at fair value	(473)	659
Derivatives [Member] | Cash Collateral Netting [Member]
Derivative [Line Items]
Cash collateral netting	(56,000)	(48,724)
Cash collateral netting	42,144	39,127
Derivatives [Member] | Level 1 [Member]
Derivative [Line Items]
Total financial assets at fair value	24	22
Total financial liabilities at fair value	(29)	(61)
Derivatives [Member] | Level 1 [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	3	12
Total financial liabilities at fair value	(3)	(24)
Derivatives [Member] | Level 1 [Member] | Equity Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	21	10
Total financial liabilities at fair value	(26)	(37)
Derivatives [Member] | Level 1 [Member] | Gross Fair Value Of Derivative [Member]
Derivative [Line Items]
Total financial assets at fair value	24	22
Total financial liabilities at fair value	(29)	(61)
Derivatives [Member] | Level 2 [Member]
Derivative [Line Items]
Total financial assets at fair value	96,101	89,259
Total financial liabilities at fair value	(80,815)	(77,961)
Derivatives [Member] | Level 2 [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	279,443	235,680
Total financial liabilities at fair value	(251,050)	(215,662)
Derivatives [Member] | Level 2 [Member] | Credit Risk Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	17,204	15,992
Total financial liabilities at fair value	(19,141)	(16,529)
Derivatives [Member] | Level 2 [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	80,178	85,837
Total financial liabilities at fair value	(81,826)	(88,663)
Derivatives [Member] | Level 2 [Member] | Commodity Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	10,648	17,193
Total financial liabilities at fair value	(15,306)	(19,808)
Derivatives [Member] | Level 2 [Member] | Equity Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	48,953	47,168
Total financial liabilities at fair value	(53,817)	(49,910)
Derivatives [Member] | Level 2 [Member] | Gross Fair Value Of Derivative [Member]
Derivative [Line Items]
Total financial assets at fair value	436,426	401,870
Total financial liabilities at fair value	(421,140)	(390,572)
Derivatives [Member] | Level 2 [Member] | Counterparty Netting in Levels [Member]
Derivative [Line Items]
Total financial assets at fair value	(340,325)	(312,611)
Total financial liabilities at fair value	340,325	312,611
Derivatives [Member] | Level 3 [Member]
Derivative [Line Items]
Total financial assets at fair value	4,654	4,948
Total financial liabilities at fair value	(4,629)	(4,358)
Derivatives [Member] | Level 3 [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	557	408
Total financial liabilities at fair value	(468)	(517)
Derivatives [Member] | Level 3 [Member] | Credit Risk Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	3,525	3,444
Total financial liabilities at fair value	(1,648)	(1,772)
Derivatives [Member] | Level 3 [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	187	681
Total financial liabilities at fair value	(398)	(220)
Derivatives [Member] | Level 3 [Member] | Commodity Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	490	431
Total financial liabilities at fair value	(243)	(319)
Derivatives [Member] | Level 3 [Member] | Equity Contract [Member]
Derivative [Line Items]
Total financial assets at fair value	687	940
Total financial liabilities at fair value	(2,664)	(2,486)
Derivatives [Member] | Level 3 [Member] | Gross Fair Value Of Derivative [Member]
Derivative [Line Items]
Total financial assets at fair value	5,446	5,904
Total financial liabilities at fair value	(5,421)	(5,314)
Derivatives [Member] | Level 3 [Member] | Counterparty Netting in Levels [Member]
Derivative [Line Items]
Total financial assets at fair value	(792)	(956)
Total financial liabilities at fair value	$ 792	$ 956