Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Intangible asset amortization expense		$ 1,277	$ 1,317	$ 1,393
Estimated amortization expense - 2021		1,262
Estimated amortization expense - 2022		1,190
Estimated amortization expense - 2023		1,108
Estimated amortization expense - 2024		986
Estimated amortization expense - 2025		906
Intangible assets with indefinite lives, excluding goodwill		18,300	19,000
Pre tax goodwill impairment	$ 10,000	$ 10,033	$ 90
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