Goodwill and other intangible assets - Intangible assets - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible asset amortization expense	$ 1,393	$ 1,469	$ 1,490
Estimated amortization expense - 2019	1,318
Estimated amortization expense - 2020	1,224
Estimated amortization expense - 2021	1,136
Estimated amortization expense - 2022	1,063
Estimated amortization expense - 2023	1,018
Intangible assets with indefinite lives, excluding goodwill	$ 18,900	$ 18,900