Investments in equity securities (Detail) - USD ($) $ in Millions	Sep. 30, 2019		Dec. 31, 2018
Summary of Investment Holdings [Line Items]
Cost Basis	$ 112,207		$ 102,867
Net Unrealized Gains	107,844		69,890
Fair Value	220,051	[1]	172,757	[2]
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	44,694		44,332
Net Unrealized Gains	51,804		38,260
Fair Value	96,498		82,592
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	38,928		38,783
Net Unrealized Gains	43,087		22,838
Fair Value	82,015		61,621
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	28,585		19,752
Net Unrealized Gains	12,953		8,792
Fair Value	$ 41,538		$ 28,544

[1] Approximately 66% of the aggregate fair value was concentrated in five companies (American Express Company – $17.9 billion; Apple Inc. – $57.0 billion; Bank of America Corporation – $27.8 billion; The Coca-Cola Company – $21.8 billion and Wells Fargo & Company – $20.2 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).