Long-term Debt (Issuance and Repurchase of Notes) (Narrative) (Details) (USD $) In Millions	3 Months Ended		1 Months Ended		1 Months Ended	12 Months Ended		1 Months Ended		1 Months Ended
	Apr. 30, 2011	May 01, 2010	Mar. 31, 2010 Fixed Rate 6.625 Percent Notes Due April 2021 [Member]	Apr. 30, 2011 Fixed Rate 6.625 Percent Notes Due April 2021 [Member]	May 31, 2010 Fixed Rate 7.00% Notes Due May 2020 [Member]	Jan. 29, 2011 Fixed Rate 7.00% Notes Due May 2020 [Member]	Apr. 30, 2011 Fixed Rate 7.00% Notes Due May 2020 [Member]	May 31, 2010 Fixed Rate 6.125% Notes Due December 2012 [Member]	Aug. 31, 2010 Fixed Rate 6.125% Notes Due December 2012 [Member]	May 31, 2010 Fixed Rate 5.25% Notes Due November 2014 [Member]	Aug. 31, 2010 Fixed Rate 5.25% Notes Due November 2014 [Member]
Debt Instrument, Face Amount			$ 1,000	$ 1,000	$ 400		$ 400
Net proceeds from the notes issuance	981	0	981		390
Notes issuance transaction costs			19		10
Debt instrument, face amount, repurchased								134	1	266	20
Payments of long-term debt	0	200						144		277
Loss on extinguishment of debt										$ 25
Maturity date			Apr. 01, 2021			May 01, 2020