Derivative Instruments (Narrative) (Details) (USD $) In Millions	1 Months Ended	3 Months Ended				1 Months Ended			1 Months Ended		1 Months Ended
	Aug. 31, 2010	Apr. 30, 2011	May 01, 2010	Jan. 31, 2007	Mar. 31, 2010 Interest Rate Swap	Mar. 31, 2010 Variable Rate Term Loan Due August 2012 [Member]	Jan. 29, 2011 2017 Notes [Member]	Jun. 30, 2010 2017 Notes [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]
Canadian dollar denominated intercompany loans related to cross-currency swaps				$ 470
Notional amount of interest rate fair value hedge terminated	21
Repurchase of notes in conjunction with termination of fair value hedges									134	1	266	20
Fair value interest rate swap arrangements							150	175
Arrangements terminated, realized losses recognized as interest expense					10
Prepayment of long-term debt		$ 0	$ 200			$ 200			$ 144		$ 277