Accounting Policies Summary of Significant Accounting Policies (Leases) (Details) - USD ($) $ in Millions	Apr. 30, 2019	Jan. 31, 2019	Apr. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total assets	$ 234,544	$ 219,295	$ 204,927
Operating lease right-of-use assets, net	16,833	0	0
Operating lease obligations	17,467
Retained earnings (net of tax)	76,276	$ 80,785	$ 82,982
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