Segment Information - Reconciliation of Reportable Segment Profit to the Statements of Operations (Details) - USD ($) $ in Millions	3 Months Ended								5 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Oct. 31, 2016
Not allocated to segments:
Stock-based compensation									$ (7)	$ (11)	$ (6)	$ (20)
Restructuring costs	$ (7)	$ (1)	$ (2)	$ 0	$ (4)	$ (3)	$ (4)	$ (3)	0	(10)	(14)	(20)
Separation and integration-related costs	(22)	(19)	(21)	(44)	(46)	(27)	(6)	(11)	(34)	(106)	(90)	(34)
Interest expense, net	(37)	(37)	(37)	(10)	(5)	0	(5)	(2)	(10)	(121)	(12)	(31)
Income before taxes	$ (13)	$ 48	$ 36	$ 41	$ 36	$ 45	$ 66	$ 52	59	112	199	129
Operating segments
Segment Reporting Information [Line Items]
Segment profit									110	527	390	234
Not allocated to segments:
Amortization of acquired intangible assets									(73)	(330)	(167)	(225)
Operating segments | Series of Individually Immaterial Business Acquisitions
Not allocated to segments:
Amortization of acquired intangible assets									0	(165)	(69)	0
Corporate
Not allocated to segments:
Stock-based compensation									(7)	(11)	(6)	(20)
Restructuring costs									0	(4)	(14)	(20)
Separation and integration-related costs									(34)	(106)	(90)	(34)
Interest expense, net									(10)	(121)	(12)	(31)
Other unallocated, net									$ 0	$ (8)	$ 0	$ 0