Goodwill and other intangible assets - Goodwill (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Goodwill And Intangible Assets Disclosure [Abstract]
Balance at beginning of year	$ 81,882	$ 81,025
Acquisitions of businesses	15	890
Other, including foreign currency translation	(238)	(33)
Balance at end of period	$ 81,659	$ 81,882