Property and Equipment - Depreciation Expense (Details) - USD ($) $ in Millions	5 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Oct. 31, 2016
Property, Plant and Equipment [Line Items]
Total depreciation expense	$ 68	$ 126	$ 69	$ 167
Depreciation expense for owned property and equipment
Property, Plant and Equipment [Line Items]
Total depreciation expense	6	9	12	14
Depreciation expense for property and equipment under capital lease
Property, Plant and Equipment [Line Items]
Total depreciation expense	$ 62	$ 117	$ 57	$ 153