Investments in equity securities (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Summary of Investment Holdings [Line Items]
Cost Basis	$ 75,506	$ 109,416
Net Unrealized Gains	196,082	244,426
Fair Value	271,588	353,842
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	15,707	27,136
Net Unrealized Gains	75,936	51,176
Fair Value	91,643	78,312
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	12,658	34,248
Net Unrealized Gains	92,091	166,895
Fair Value	104,749	201,143
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	47,141	48,032
Net Unrealized Gains	28,055	26,355
Fair Value	$ 75,196	$ 74,387