Additional Financial Information (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Cash and Cash Equivalents [Line Items]
Document Period End Date	Dec. 31, 2019
Cash and Cash Equivalents	$ 3,179	$ 6,982	$ 6,285	$ 6,659
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	3,267	7,063	$ 6,285	$ 6,659
Checks Issued In Excess Of Associated Bank Balances But Not Yet Presented For Collection	74	75
Other Assets [Member]
Cash and Cash Equivalents [Line Items]
Restricted Cash, Current	$ 88	$ 81