Goodwill and other intangible assets - Goodwill (Detail) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2024		Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Balance at the beginning of the year		$ 84,626	[1]	$ 78,119
Business acquisitions		1		7,347
Other, including acquisition period remeasurements and foreign currency translation		(78)		(840)
Balance at the end of the period	[1]	$ 84,549		$ 84,626

[1] Net of accumulated goodwill impairments of $11.1 billion as of March 31, 2024 and December 31, 2023.