Long-term Debt Schedule of Debt Maturities (Details) £ in Millions, $ in Millions	9 Months Ended
	Oct. 31, 2017 USD ($)	Oct. 31, 2016 USD ($)	Oct. 24, 2017 USD ($)	Jul. 06, 2017 GBP (£)	Apr. 21, 2017 USD ($)	Apr. 05, 2017 USD ($)
Debt Instrument [Line Items]
Repayments of Long-term Debt	$ 8,859	$ 2,040
Unsecured debt
Debt Instrument [Line Items]
Repayments of Long-term Debt	8,824
Repayments of Long-Term Debt, Matured	1,500
Repayment of Long-Term Debt, Partial Extinguishment	7,324
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 | 4.125% Fixed Rate Debt, Due 2019 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 500
Interest Rate			4.125%
Repayments of Long-term Debt	135
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	660
Unsecured debt | 5.875% Fixed Rate Debt, Due 2027 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 750
Interest Rate			5.875%
Repayments of Long-term Debt	207
Unsecured debt | 5.250% Fixed Rate Debt, Due 2035 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 2,500
Interest Rate			5.25%
Repayments of Long-term Debt	407
Unsecured debt | 6.500% Fixed Rate Debt, Due 2037 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 3,000
Interest Rate			6.50%
Repayments of Long-term Debt	1,549
Unsecured debt | 6.200% Fixed Rate Debt, Due 2038 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 2,000
Interest Rate			6.20%
Repayments of Long-term Debt	887
Unsecured debt | 4.875% Fixed Rate Debt, Due 2039 [Member]
Debt Instrument [Line Items]
Principal Amount | £				£ 1,000
Interest Rate				4.875%
Repayments of Long-term Debt	459
Unsecured debt | 5.625% Fixed Rate Debt, Due 2040 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 1,250
Interest Rate			5.625%
Repayments of Long-term Debt	382
Unsecured debt | 4.875% Fixed Rate Debt, Due 2040 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 750
Interest Rate			4.875%
Repayments of Long-term Debt	277
Unsecured debt | 5.000% Fixed Rate Debt, Due 2040 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 1,250
Interest Rate			5.00%
Repayments of Long-term Debt	605
Unsecured debt | 5.625% Fixed Rate Debt, Due 2041 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 2,000
Interest Rate			5.625%
Repayments of Long-term Debt	680
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	290
Unsecured debt | 4.750% Fixed Rate Debt, Due 2043 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 750
Interest Rate			4.75%
Repayments of Long-term Debt	317
Unsecured debt | 4.300% Fixed Rate Debt, Due 2044 [Member]
Debt Instrument [Line Items]
Principal Amount			$ 1,000
Interest Rate			4.30%
Repayments of Long-term Debt	$ 469