Accounting Policies Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)	3 Months Ended	6 Months Ended
	Apr. 30, 2018	Jul. 31, 2018	Feb. 01, 2019	Jan. 31, 2018	Jul. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		$ 924,000,000
Contract with customer, liability	$ 1,853,000,000			$ 2,000,000,000
Restricted Cash		$ 22,000,000		$ 300,000,000	$ 300,000,000
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 2,600,000,000
Subsequent Event [Member] | Minimum [Member] | Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ 14,000,000,000
Subsequent Event [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ 18,000,000,000