Financing (Narrative) (Details) (USD $)	1 Months Ended		6 Months Ended
	Sep. 05, 2011	May 28, 2011	Jul. 30, 2011	Jul. 31, 2010
Debt repaid in period			$ 330,000,000	$ 76,000,000
Debt instrument, principal outstanding			612,000,000
Decrease in interest payable effective rate		0.25%
Effective interest rate of debt instrument		8.125%
Maximum potential increase in debt interest rate due to potential downgrades in debt ratings		1.75%
Maximum potential decrease in debt interest rate due to potential upgrades in debt ratings		0.25%
Cash paid for repurchase of Company debt				526,000,000
Amount of outstanding debt repurchased before maturity				500,000,000
Additional interest expense from early repurchase of debt				27,000,000
Shares of common stock acquired	1,361,000
Cost of acquired shares	35,000,000
Amount of authorizations unused	817,000,000
Letter Of Credit Agreement Expiring On June 20, 2015 [Member]
Line of credit facility, maximum borrowing capacity			1,500,000,000
Line of credit facility, maximum borrowing capacity at Company's option			1,750,000,000
Line of credit facility, expiration date			June 20, 2015
Line of credit facility, amount outstanding			0
Letter Of Credit Agreement Expiring On August 30,2012 [Member]
Line of credit facility, maximum borrowing capacity			2,000,000,000
Line of credit facility, expiration date			August 30, 2012
Line of credit facility, amount outstanding			$ 0