Leases - Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2021	Mar. 31, 2021
Operating Lease, Supplemental Balance Sheet Information [Abstract]
Operating right-of-use assets, net	$ 1,122	$ 1,366
Current operating lease liabilities	386	418
Non-current operating lease liabilities	805	1,038
Total operating lease liabilities	$ 1,191	$ 1,456
Weighted-average operating lease term	4 years 6 months	4 years 10 months 24 days
Weighted-average operating lease discount rate	3.30%	3.80%
Finance Lease, Supplemental Balance Sheet Information [Abstract]
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Property and equipment, net of accumulated depreciation of $4,062 and $4,121	Property and equipment, net of accumulated depreciation of $4,062 and $4,121
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Short-term debt and current maturities of long-term debt	Short-term debt and current maturities of long-term debt
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Long-term Debt, Excluding Current Maturities	Long-term Debt, Excluding Current Maturities
ROU finance lease assets	$ 713	$ 834
Finance lease, liability, current	304	398
Finance lease, liability, noncurrent	367	496
Total finance lease liabilities	$ 671	$ 894
Weighted-average finance lease term	2 years 8 months 12 days	2 years 7 months 6 days
Weighted-average finance lease discount rate	3.00%	3.60%