Notes Payable and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	1 Months Ended
	Jul. 30, 2011	Jul. 30, 2011	Jul. 31, 2011 Fixed rate unsecured debt	Jul. 31, 2011 Floating rate unsecured debt
Notes Payable and Long-Term Debt
Maximum amount outstanding during the period	$ 850	$ 850
Average amount outstanding during the period	329	164
Debt Maturities
Unsecured debt, amount issued			$ 350	$ 650
Unsecured debt, fixed interest rate (as a percent)			1.125%
Variable interest rate used				three-month LIBOR
Basis spread on variable rate used (as a percent)				0.17%