Divestitures - Cash Flow (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation	$ 643	$ 820	$ 709
Capital expenditures	(350)	(297)	$ (224)	[1]
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]
Depreciation	16	70
Amortization	17	99
Capital expenditures	0	(18)
Gain on dispositions	$ 24	$ 0

[1] As a result of the USPS Separation, the Consolidated Statements of Operations, Consolidated Balance Sheets, and related financial information reflect USPS's operations and assets and liabilities as discontinued operations for all periods presented. The cash flows of USPS have not been segregated and are included in the Consolidated Statement of Cash flows for the fiscal year ended March 31, 2018 and through the separation date of May 31, 2018 in the Consolidated Statement of Cash Flows for the fiscal year ended March 31, 2019.