Goodwill and other intangible assets - Goodwill (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Jun. 30, 2020	Dec. 31, 2021		Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Balance at beginning of year			$ 73,734	[1]	$ 81,882
Business acquisitions			353		1,758
Impairment charges		$ (10,000)			(10,033)
Other, including foreign currency translation			(212)		127
Balance at end of year	[1]		$ 73,875		$ 73,734

[1] Net of accumulated goodwill impairments of $11.0 billion as of December 31, 2021 and 2020.