Short-term Borrowings and Long-term Debt (Schedule of Fiscal Year 2019 and 2018 Debt Maturities) (Details) £ in Millions, $ in Millions	12 Months Ended
	Jan. 31, 2019 USD ($)	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)	Dec. 15, 2018 USD ($)	Jun. 01, 2018 USD ($)	Apr. 11, 2018 USD ($)	Feb. 15, 2018 USD ($)	Jan. 25, 2018 USD ($)	Jan. 25, 2018 GBP (£)	Nov. 06, 2017 USD ($)	Apr. 21, 2017 USD ($)	Apr. 05, 2017 USD ($)
Debt Instrument [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost	$ 0	$ 3,059	$ 0
Repayments of long-term debt	3,784	13,061	$ 2,055
Unsecured debt
Debt Instrument [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost		11,272
Repayments of long-term debt	3,784	13,061
Repayments of Unsecured Debt		1,789
Unsecured debt | 5.800% Fixed Rate Debt, Due 2018 [Member]
Debt Instrument [Line Items]
Principal amount							$ 1,250
Interest rate							5.80%
Repayments of long-term debt	1,250
Unsecured debt | 1.125% Fixed Rate Debt, Due 2018 [Member]
Debt Instrument [Line Items]
Principal amount						$ 1,250
Interest rate						1.125%
Repayments of long-term debt	1,250
Unsecured debt | Variable Rate Debt, Due 2018 [Domain]
Debt Instrument [Line Items]
Principal amount					$ 500
Repayments of long-term debt	500
Unsecured debt | 1.950% Fixed Rate Debt, Due 2018 [Member]
Debt Instrument [Line Items]
Principal amount				$ 724
Interest rate				0.00%
Repayments of long-term debt	724
Unsecured debt | Variable Rate Debt (60 USD), Due 2019 [Domain]
Debt Instrument [Line Items]
Principal amount	60
Repayments of long-term debt	$ 60
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 (500 USD), Due 2017 [Domain]
Debt Instrument [Line Items]
Principal amount											$ 500
Interest rate											1.00%
Repayments of long-term debt		500
Unsecured debt | Variable Rate Deb (289 USD), Due 2018 [Domain]
Debt Instrument [Line Items]
Principal amount		289
Repayments of long-term debt		289
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
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]
Principal amount | £									£ 1,000
Interest rate								5.25%	5.25%
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