Basis of Presentation - Credit loss adoption (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounting change
Adoption of new accounting standard	$ 7,157	$ 6,893		$ 7,070	$ 6,787	$ 6,467	$ 6,276
Allowance for doubtful accounts	34			$ 28	$ 27		$ 29
Cumulative Effect, Period of Adoption, Adjustment [Member]
Accounting change
Adoption of new accounting standard	(2)
Accounting Standards Update 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
Accounting change
Adoption of new accounting standard			$ (2)
Allowance for doubtful accounts	$ (1)		$ (1)