Investments in equity securities (Detail) - USD ($) $ in Millions	Mar. 31, 2021		Dec. 31, 2020
Summary of Investment Holdings [Line Items]
Cost Basis	$ 106,451		$ 108,620
Net Unrealized Gains	175,646		172,550
Fair Value	282,097	[1]	281,170	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	26,730		26,312
Net Unrealized Gains	52,081		40,167
Fair Value	78,811		66,479
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	34,787		34,747
Net Unrealized Gains	101,445		111,583
Fair Value	136,232		146,330
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	44,934		47,561
Net Unrealized Gains	22,120		20,800
Fair Value	$ 67,054		$ 68,361

[1] Approximately 69% of the aggregate fair value was concentrated in four companies (American Express Company – $21.4 billion; Apple Inc. – $110.9 billion; Bank of America Corporation – $40.0 billion and The Coca-Cola Company – $21.1 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).