Accounting Policies Summary of Significant Accounting Policies (Leases) (Details) - USD ($) $ in Millions	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Jul. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total assets	$ 234,861		$ 219,295	$ 206,062
Operating lease right-of-use assets, net	17,239		0	0
Operating lease obligations	17,874
Retained earnings (net of tax)	$ 78,432		$ 80,785	$ 80,810
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total assets		$ 14,800
Total liabilities		15,100
Operating lease right-of-use assets, net		16,800
Operating lease obligations		17,500
Build-to-suit assets derecognized, net		(2,200)
Build-to-suit liabilities derecognized		(1,700)
Retained earnings (net of tax)		$ 300