Segment Information - Reconciliation of Operating Revenues (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	$ 32,203	$ 30,548	$ 63,975	$ 60,362
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	29,908	29,001	59,365	57,561
Corporate and other
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	2,680	1,778	5,391	3,238
Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	(385)	(351)	(781)	(751)
Operating results from divested businesses
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment reporting information, revenue	$ 0	$ 120	$ 0	$ 314