Segment Information - Schedule of Segment Reporting Information, by Segment (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Interest expense	$ 147	$ 142	$ 434	$ 422
Operating Segments
Segment Reporting Information [Line Items]
Interest income	2	4	7	15
Interest expense	$ 8	$ 13	$ 29	$ 39