Divestitures - Income Statement (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total income from discontinued operations	$ 35	$ 236	$ 0
USPS Separation | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	431	2,823
Costs of services	311	2,104
Selling, general and administrative	50	152
Depreciation and amortization	33	169
Restructuring costs	1	14
Interest expense	8	15
Other income, net	(25)	2
Total costs and expenses	378	2,456
Total income from discontinued operations, before income taxes	53	367
Income tax expense	18	131
Total income from discontinued operations	$ 35	$ 236