Debt - Components of Long Term Debt (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Aug. 31, 2015	Oct. 31, 2015	Aug. 01, 2015	Nov. 01, 2014	Oct. 31, 2015	Nov. 01, 2014	Jan. 31, 2015
Debt Instrument [Line Items]
Long-term Debt, Fair Value		$ 2,900		$ 3,100	$ 2,900	$ 3,100	$ 3,100
Long-term Debt, Current Maturities			$ 317
Unamortized debt discount		5		7	5	7	7
Deferred Finance Costs, Net		(18)		(14)	(18)	(14)	(13)
Long-term debt		2,792		2,779	2,792	2,779	2,780
Repayments of Debt		(318)	767
Gains (Losses) on Extinguishment of Debt		38	131	0	169	0
Payments of Debt Extinguishment Costs			126		$ 163	0
Redemption Premium	$ (37)
Write off of Deferred Debt Issuance Cost	$ 1		5
Line of Credit Facility, Description					1.0
Short-term Debt		$ 400		0	$ 400	0	0
Senior Notes Due Twenty Twenty Five [Member] | Senior Notes
Debt Instrument [Line Items]
Total senior debt			$ 650
Senior Notes
Debt Instrument [Line Items]
Effective Rate		5.00%			5.00%
Total senior debt		$ 2,815		2,800	$ 2,815	2,800	2,800
Senior Notes | Senior Notes Due 2017
Debt Instrument [Line Items]
Effective Rate		0.00%			0.00%
Debt Instrument, Interest Rate, Stated Percentage		0.00%	6.00%		0.00%
Total senior debt		$ 0		650	$ 0	650	650
Senior Notes | Senior Notes Due Two Thousand And Twenty One [Member]
Debt Instrument [Line Items]
Effective Rate		5.00%			5.00%
Debt Instrument, Interest Rate, Stated Percentage		4.00%			4.00%
Total senior debt		$ 650		650	$ 650	650	650
Senior Notes | Senior Notes Due 2023
Debt Instrument [Line Items]
Effective Rate		3.00%			3.00%
Debt Instrument, Interest Rate, Stated Percentage		3.00%			3.00%
Total senior debt		$ 350		350	$ 350	350	350
Senior Notes | Senior Notes Due Twenty Twenty Three [Member]
Debt Instrument [Line Items]
Effective Rate		5.00%			5.00%
Debt Instrument, Interest Rate, Stated Percentage		5.00%			5.00%
Total senior debt		$ 300		300	$ 300	300	300
Senior Notes | Senior Notes Due Twenty Twenty Five [Member]
Debt Instrument [Line Items]
Effective Rate		4.00%			4.00%
Debt Instrument, Interest Rate, Stated Percentage		4.00%	4.00%		4.00%
Total senior debt		$ 650		0	$ 650	0	0
Senior Notes | Senior Notes Due 2029
Debt Instrument [Line Items]
Effective Rate		7.00%			7.00%
Debt Instrument, Interest Rate, Stated Percentage		7.00%			7.00%
Total senior debt		$ 99		200	$ 99	200	200
Senior Notes | Senior Notes Due 2033
Debt Instrument [Line Items]
Effective Rate		6.00%			6.00%
Debt Instrument, Interest Rate, Stated Percentage		6.00%			6.00%
Total senior debt		$ 166		300	$ 166	300	300
Senior Notes | Senior Notes Due 2037
Debt Instrument [Line Items]
Effective Rate		7.00%			7.00%
Debt Instrument, Interest Rate, Stated Percentage		7.00%			7.00%
Total senior debt		$ 150		350	$ 150	350	350
Senior Notes | Senior Notes Due 2045
Debt Instrument [Line Items]
Effective Rate		6.00%			6.00%
Debt Instrument, Interest Rate, Stated Percentage		6.00%	6.00%		6.00%
Total senior debt		$ 450	$ 450	$ 0	$ 450	$ 0	$ 0