Investments in equity securities (Detail) - USD ($) $ in Millions	Mar. 31, 2020		Dec. 31, 2019
Summary of Investment Holdings [Line Items]
Cost Basis	$ 113,249		$ 110,340
Net Unrealized Gains/(losses)	67,533		137,687
Fair Value	180,782	[1]	248,027	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	40,845		40,419
Net Unrealized Gains/(losses)	22,046		61,976
Fair Value	62,891		102,395
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	38,887		38,887
Net Unrealized Gains/(losses)	45,713		60,747
Fair Value	84,600		99,634
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	33,517		31,034
Net Unrealized Gains/(losses)	(226)		14,964
Fair Value	$ 33,291		$ 45,998

[1] Approximately 69% of the aggregate fair value was concentrated in five companies (American Express Company – $13.0 billion; Apple Inc. – $63.8 billion; Bank of America Corporation – $20.2 billion; The Coca-Cola Company – $17.7 billion and Wells Fargo & Company – $9.9 billion).

[2] Approximately 67% of the aggregate fair value was concentrated in five companies (American Express Company – $18.9 billion; Apple Inc. – $73.7 billion; Bank of America Corporation – $33.4 billion; The Coca-Cola Company – $22.1 billion and Wells Fargo & Company – $18.6 billion).