Investments in equity securities (Detail) - USD ($) $ in Millions	Dec. 31, 2019		Dec. 31, 2018
Summary of Investment Holdings [Line Items]
Cost Basis	$ 110,340		$ 102,867
Net Unrealized Gains	137,687		69,890
Fair Value	248,027	[1]	172,757	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	40,419		44,332
Net Unrealized Gains	61,976		38,260
Fair Value	102,395		82,592
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	38,887		38,783
Net Unrealized Gains	60,747		22,838
Fair Value	99,634		61,621
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	31,034		19,752
Net Unrealized Gains	14,964		8,792
Fair Value	$ 45,998		$ 28,544

[1] 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).

[2] Approximately 68% of the aggregate fair value was concentrated in five companies (American Express Company – $14.5 billion; Apple Inc. – $40.3 billion; Bank of America Corporation – $22.6 billion; The Coca-Cola Company – $18.9 billion and Wells Fargo & Company – $20.7 billion).