Investments in equity securities (Detail) - USD ($) $ in Millions	Jun. 30, 2021		Dec. 31, 2020
Summary of Investment Holdings [Line Items]
Cost Basis	$ 105,219		$ 108,620
Net Unrealized Gains	202,723		172,550
Fair Value	307,942	[1]	281,170	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	27,384		26,312
Net Unrealized Gains	59,237		40,167
Fair Value	86,621		66,479
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	34,885		34,747
Net Unrealized Gains	115,926		111,583
Fair Value	150,811		146,330
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	42,950		47,561
Net Unrealized Gains	27,560		20,800
Fair Value	$ 70,510		$ 68,361

[1] Approximately 69% of the aggregate fair value was concentrated in four companies (American Express Company – $25.1 billion; Apple Inc. – $124.3 billion; Bank of America Corporation – $42.6 billion and The Coca-Cola Company – $21.6 billion).

[2] Approximately 68% of the aggregate fair value was concentrated in four companies (American Express Company – $18.3 billion; Apple Inc. – $120.4 billion; Bank of America Corporation – $31.3 billion and The Coca-Cola Company – $21.9 billion).