Leases - Supplemental balance sheet information (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019
Leases [Abstract]
Operating lease right-of-use assets	$ 2,100	$ 1,886	$ 2,100
Current portion of operating lease liabilities	390	354
Long-term operating lease liabilities	1,867	1,660
Total operating lease liabilities	2,257	2,014	$ 2,200
Property, plant and equipment, net	237	180
Current portion of long-term debt	22	15
Long-term debt	206	151
Total finance lease liabilities	$ 228	$ 166
Weighted average remaining lease term (Years) - Operating leases	7 years 9 months 18 days	7 years 8 months 12 days
Weighted average remaining lease term (Years) - Finance leases	10 years 1 month 6 days	12 years 1 month 6 days
Weighted average discount rate - Operating leases (percent)	2.53%	3.03%
Weighted average discount rate - Finance leases (percent)	2.71%	2.86%