Long-Term Debt (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Jun. 06, 2011
Apr. 30, 2011
Oct. 31, 2010
Nov. 25, 2008
Apr. 30, 2011
Senior Notes 2012 [Member]
Apr. 30, 2011
Senior Notes 2012 [Member]
Oct. 31, 2010
Senior Notes 2012 [Member]
Apr. 30, 2011
Senior Notes 2013 [Member]
Oct. 31, 2010
Senior Notes 2013 [Member]
Apr. 30, 2011
Senior Notes 2015 [Member]
Apr. 30, 2011
Senior Notes 2015 [Member]
Oct. 31, 2010
Senior Notes 2015 [Member]
Jun. 06, 2011
Senior Notes 2015 [Member]
Apr. 30, 2011
Senior Notes 2017 [Member]
Oct. 31, 2010
Senior Notes 2017 [Member]
Apr. 30, 2011
Senior Notes 2020 [Member]
Apr. 30, 2011
Senior Notes 2020 [Member]
Oct. 31, 2010
Senior Notes 2020 [Member]
Apr. 30, 2011
Senior Notes 2012 And 2015 [Member]
Apr. 30, 2011
Senior Notes 2012 And 2015 [Member]
Oct. 31, 2010
Senior Notes 2012 And 2015 [Member]
Apr. 30, 2011
Senior Notes 2013 And 2020 [Member]
Oct. 31, 2010
Senior Notes 2013 And 2020 [Member]
Debt Instrument [Line Items]                                              
Carrying value of debt   $ 2,144 $ 2,190     $ 254 $ 256 $ 249 $ 249   $ 521 $ 536   $ 631 $ 633   $ 489 $ 516          
Issuance date of debt           September 2009 September 2009 July 2010 July 2010   September 2009 September 2009   October 2007 October 2007   July 2010 July 2010          
Interest rate swap   50 96     4 6 0 0   22 37   33 35   (9) 18          
Amortized principal   2,094 2,094     250 250 249 249   499 499   598 598   498 498          
Aggregate face amount of senior notes           250 250 250 250   500 500   600 600   500 500          
Issue rate percentage of face amount (in hundredths)           99.91% 99.91% 99.82% 99.82%   99.69% 99.69%   99.60% 99.60%   99.54% 99.54%          
Maturity date Sep. 14, 2012 Sep. 14, 2012 Jul. 15, 2013 Jul. 15, 2013 Sep. 14, 2015 Sep. 14, 2015 Nov. 01, 2017 Nov. 01, 2017 Jul. 15, 2020 Jul. 15, 2020
Fixed interest rate per annum (in hundredths)           4.45% 4.45% 2.50% 2.50%   5.50% 5.50%   6.50% 6.50%   5.00% 5.00%          
Interest payment frequency           semi-annually semi-annually semi-annually semi-annually   semi-annually semi-annually   semi-annually semi-annually   semi-annually semi-annually          
Date payments commenced           March 14, 2010 March 14, 2010 January 15, 2011 January 15, 2011   March 14, 2010 March 14, 2010   May 1, 2008 May 1, 2008   January 15, 2011 January 15, 2011          
Semi-annual interest payment dates           March 14th and September 14th March 14th and September 14th January 15th and July 15th January 15th and July 15th   March 14th and September 14th March 14th and September 14th   May 1st and November 1st May 1st and November 1st   January 15th and July 15th January 15th and July 15th          
Issuance cost incurred on senior notes offered                           5 5         5 5 5 5
Schedule Of Interest Rate Swaps Regarding Senior Notes Offered [Line Items]                                              
Interest swaps terminated date Nov. 25, 2008 Jun. 06, 2011
Notional amount of terminated interest rate swaps 500 400   400                 500                    
Number of interest swaps terminated on specified date       2                                      
Asset value of terminated interest rate swaps 31 43   43                 31                    
Unamortized deferred gain on discontinued interest rate fair value hedge   33                                          
Notional amount of interest rate swaps   1,250                           500     750        
Basis points charged in calculating the interest rate (plus US dollar LIBOR) on Interest rate swaps         258         253           179              
Fair value of swaps at period end                                     26        
Fair value of derivative liability                               $ (9)             Â