Segment, Geographic and Other Revenue Information - Narrative (Detail) $ in Millions		3 Months Ended		9 Months Ended
		Mar. 31, 2019 Operating_Segment	Oct. 01, 2017 USD ($)	Sep. 30, 2018 USD ($) Operating_Segment	Oct. 01, 2017 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | Operating_Segment				2
Assets	[1]			$ 167,838		$ 171,797
Forecast [Member]
Segment Reporting Information [Line Items]
Number of business segments | Operating_Segment		3
Adjustment [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Costs			$ (19)		$ (40)
Adjustment [Member] | IH [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Costs			(125)		(344)
Adjustment [Member] | EH [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Costs			$ (36)		$ (114)

[1] Amounts may not add due to rounding.