Leases - Balance Sheet Information (Details) $ in Millions	Jan. 31, 2020 USD ($)
Assets
Operating lease right-of-use assets	$ 3,891
Finance lease assets	555
Total lease assets	4,446
Liabilities
Current operating lease liabilities	501
Current maturities of long-term debt	72
Noncurrent operating lease liabilities	3,943
Long-term debt, excluding current maturities	612
Total lease liabilities	5,128
Accumulated amortization	$ 42