Short-term Borrowings and Long-term Debt (Schedule of Fiscal Year 2018 and 2017 Debt Maturities) (Details) £ in Millions, $ in Millions	12 Months Ended
	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)	Jan. 31, 2016 USD ($)	Jan. 25, 2018 USD ($)	Jan. 25, 2018 GBP (£)	Nov. 06, 2017 USD ($)	Apr. 21, 2017 USD ($)	Apr. 05, 2017 USD ($)	Apr. 15, 2016 USD ($)	Apr. 11, 2016 USD ($)
Debt Instrument [Line Items]
Repayments of long-term debt	$ 13,061	$ 2,055	$ 4,432
Unsecured debt
Debt Instrument [Line Items]
Repayments of long-term debt	12,772	2,000
Repayments of long-term debt, matured	1,500
Repayment of long-term debt, partial extinguishment	11,272
Unsecured debt | 5.375% Fixed Rate Debt, Due 2017 [Member]
Debt Instrument [Line Items]
Principal amount								$ 1,000
Interest rate								5.375%
Repayments of long-term debt	1,000
Unsecured debt | 1.000% Fixed Rate Debt, Due 2017 [Member]
Debt Instrument [Line Items]
Principal amount							$ 500
Interest rate							1.00%
Repayments of long-term debt	500
Unsecured debt | 1.950% Fixed Rate Debt, Due 2018 [Member]
Debt Instrument [Line Items]
Principal amount				$ 1,000
Interest rate				1.95%	1.95%
Repayments of long-term debt	276
Unsecured debt | 4.125% Fixed Rate Debt, Due 2019 [Member]
Debt Instrument [Line Items]
Principal amount						$ 500
Interest rate						4.125%
Repayments of long-term debt	136
Unsecured debt | 3.625% Fixed Rate Debt, Due 2020 [Member]
Debt Instrument [Line Items]
Principal amount						$ 1,500
Interest rate						3.625%
Repayments of long-term debt	661
Unsecured debt | 3.250% Fixed Rate Debt, Due 2020 [Member]
Debt Instrument [Line Items]
Principal amount				$ 1,750
Interest rate				3.25%	3.25%
Repayments of long-term debt	553
Unsecured debt | 4.250% Fixed Rate Debt, Due 2021 [Member]
Debt Instrument [Line Items]
Principal amount				$ 1,000
Interest rate				4.25%	4.25%
Repayments of long-term debt	491
Unsecured debt | 6.750% Fixed Rate Date, Due 2023 [Member]
Debt Instrument [Line Items]
Principal amount				$ 250
Interest rate				6.75%	6.75%
Repayments of long-term debt	98
Unsecured debt | 5.875% Fixed Rate Debt, Due 2027 [Member]
Debt Instrument [Line Items]
Principal amount				$ 750
Interest rate				5.875%	5.875%
Repayments of long-term debt	267
Unsecured debt | 7.550% Fixed Rate Debt, Due 2030 [Member]
Debt Instrument [Line Items]
Principal amount				$ 500
Interest rate				7.55%	7.55%
Repayments of long-term debt	412
Unsecured debt | 5.250% Fixed Rate Debt, Due 2035 [Member]
Debt Instrument [Line Items]
Principal amount				$ 2,500	£ 1,000
Interest rate				5.25%	5.25%
Repayments of long-term debt	532
Unsecured debt | 5.250% Fixed Rate Debt (GBP), Due 2035 [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	260
Unsecured debt | 6.500% Fixed Rate Debt, Due 2037 [Member]
Debt Instrument [Line Items]
Principal amount				$ 3,000
Interest rate				6.50%	6.50%
Repayments of long-term debt	1,700
Unsecured debt | 6.200% Fixed Rate Debt, Due 2038 [Member]
Debt Instrument [Line Items]
Principal amount				$ 2,000
Interest rate				6.20%	6.20%
Repayments of long-term debt	1,081
Unsecured debt | 4.875% Fixed Rate Debt, Due 2039 [Member]
Debt Instrument [Line Items]
Principal amount | £					£ 1,000
Interest rate				4.875%	4.875%
Repayments of long-term debt	851
Unsecured debt | 5.625% Fixed Rate Debt, Due 2040 [Member]
Debt Instrument [Line Items]
Principal amount				$ 1,250
Interest rate				5.625%	5.625%
Repayments of long-term debt	499
Unsecured debt | 4.875% Fixed Rate Debt, Due 2040 [Member]
Debt Instrument [Line Items]
Principal amount				$ 750
Interest rate				4.875%	4.875%
Repayments of long-term debt	372
Unsecured debt | 5.000% Fixed Rate Debt, Due 2040 [Member]
Debt Instrument [Line Items]
Principal amount				$ 1,250
Interest rate				5.00%	5.00%
Repayments of long-term debt	731
Unsecured debt | 5.625% Fixed Rate Debt, Due 2041 [Member]
Debt Instrument [Line Items]
Principal amount				$ 2,000
Interest rate				5.625%	5.625%
Repayments of long-term debt	1,082
Unsecured debt | 4.000% Fixed Rate Debt, Due 2043 [Member]
Debt Instrument [Line Items]
Principal amount						$ 1,000
Interest rate						4.00%
Repayments of long-term debt	291
Unsecured debt | 4.750% Fixed Rate Debt, Due 2043 [Member]
Debt Instrument [Line Items]
Principal amount				$ 750
Interest rate				4.75%	4.75%
Repayments of long-term debt	481
Unsecured debt | 4.300% Fixed Rate Debt, Due 2044 [Member]
Debt Instrument [Line Items]
Principal amount				$ 1,000
Interest rate				4.30%	4.30%
Repayments of long-term debt	$ 498
Unsecured debt | 0.600% Fixed Rate Debt, Due 2016 [Member]
Debt Instrument [Line Items]
Principal amount										$ 1,000
Interest rate										0.60%
Repayments of long-term debt		1,000
Unsecured debt | 2.800% Fixed Rate Debt, Due 2016 [Member]
Debt Instrument [Line Items]
Principal amount									$ 1,000
Interest rate									2.80%
Repayments of long-term debt		$ 1,000