Investments in equity securities (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Summary of Investment Holdings [Line Items]
Cost Basis	$ 77,125	$ 75,506
Net Unrealized Gains	186,610	196,082
Fair Value	263,735	271,588
Banks, insurance and finance [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	14,268	15,707
Net Unrealized Gains	69,229	75,936
Fair Value	83,497	91,643
Consumer products [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	13,760	12,658
Net Unrealized Gains	87,110	92,091
Fair Value	100,870	104,749
Commercial, industrial and other [Member]
Summary of Investment Holdings [Line Items]
Cost Basis	49,097	47,141
Net Unrealized Gains	30,271	28,055
Fair Value	$ 79,368	$ 75,196