Investments in equity securities (Detail) - USD ($) $ in Millions	Jun. 30, 2019		Dec. 31, 2018
Summary of Investment Holdings [Line Items]
Cost Basis	$ 102,620		$ 102,867
Net Unrealized Gains	97,896		69,890
Fair Value	200,516	[1]	172,757	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	45,796		44,332
Net Unrealized Gains	50,659		38,260
Fair Value	96,455		82,592
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	39,008		38,783
Net Unrealized Gains	35,064		22,838
Fair Value	74,072		61,621
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	17,816		19,752
Net Unrealized Gains	12,173		8,792
Fair Value	$ 29,989		$ 28,544

[1] Approximately 69% of the aggregate fair value was concentrated in five companies (American Express Company – $18.7 billion; Apple Inc. – $50.5 billion; Bank of America Corporation – $27.6 billion; The Coca-Cola Company – $20.4 billion and Wells Fargo & Company – $20.5 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).