Investments in equity securities (Detail) - USD ($) $ in Millions	Jun. 30, 2020		Dec. 31, 2019
Summary of Investment Holdings [Line Items]
Cost Basis	$ 96,063		$ 110,340
Net Unrealized Gains	111,391		137,687
Fair Value	207,454	[1]	248,027	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	31,164		40,419
Net Unrealized Gains	28,081		61,976
Fair Value	59,245		102,395
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	38,706		38,887
Net Unrealized Gains	73,990		60,747
Fair Value	112,696		99,634
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	26,193		31,034
Net Unrealized Gains	9,320		14,964
Fair Value	$ 35,513		$ 45,998

[1] Approximately 71% of the aggregate fair value was concentrated in four companies (American Express Company – $14.4 billion; Apple Inc. – $91.5 billion; Bank of America Corporation – $22.6 billion and The Coca-Cola Company – $17.9 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).