Segment Information - Reconciliation of Operating Revenues (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	$ 32,607	$ 31,717	$ 96,582	$ 92,079
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	30,344	29,242	89,709	86,803
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	2,655	2,796	8,046	6,034
Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	(392)	(375)	(1,173)	(1,126)
Operating results from divested businesses
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	$ 0	$ 54	$ 0	$ 368