Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Goodwill [Line Items]
Intangible asset amortization expense		$ 637	$ 647
Intangible assets with indefinite lives, excluding goodwill		$ 18,300		$ 18,300
Pre tax goodwill impairment	$ 10,000			$ 10,033
Pre tax intangible assets impairment charges	638
PCC [Member]
Goodwill [Line Items]
Pre tax impairment charges	10,000
Goodwill and indefinite-lived intangible assets	$ 31,000		$ 31,000