Summary of Significant Accounting Policies (Advertising Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Operating Expenses [Abstract]
Advertising expense, net of vendor reimbursements	$ 396	$ 222	$ 195
Cooperative Advertising Amount	$ 37	$ 22	$ 38