Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	2 Months Ended
	May 05, 2012	Apr. 30, 2011
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation.
Balance at the beginning of the period	$ 82	$ 110
Changes in unrealized losses included in other comprehensive income	1	1
Sales	(17)	(14)
Balance at the end of the period	66	97
Student loan bonds [Member]
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation.
Balance at the beginning of the period	80	108
Changes in unrealized losses included in other comprehensive income	1	1
Sales	(17)	(14)
Balance at the end of the period	64	95
Municipal revenue bonds [Member]
Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation.
Balance at the beginning of the period	2	2
Changes in unrealized losses included in other comprehensive income	0	0
Sales	0	0
Balance at the end of the period	$ 2	$ 2