Investments in equity securities (Detail) - USD ($) $ in Millions	Dec. 31, 2020		Dec. 31, 2019
Summary of Investment Holdings [Line Items]
Cost Basis	$ 108,620		$ 110,340
Net Unrealized Gains	172,550		137,687
Fair Value	281,170	[1]	248,027	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	26,312		40,419
Net Unrealized Gains	40,167		61,976
Fair Value	66,479		102,395
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	34,747		38,887
Net Unrealized Gains	111,583		60,747
Fair Value	146,330		99,634
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	47,561		31,034
Net Unrealized Gains	20,800		14,964
Fair Value	$ 68,361		$ 45,998

[1] 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).

[2] Approximately 60% of the aggregate fair value was concentrated in four companies (American Express Company – $18.9 billion; Apple Inc. – $73.7 billion; Bank of America Corporation – $33.4 billion and The Coca-Cola Company – $22.1 billion).