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Postretirement Plans (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2010
Postretirement Benefit Plans [Line Items]      
Deferred actuarial gains in accumulated other comprehensive income $ (1,982)    
Gains that will be amortized into earnings in 2013 (244)    
Postretirement Plans [Member]
     
Postretirement Benefit Plans [Line Items]      
Deferred actuarial gains in accumulated other comprehensive income 99    
Gains that will be amortized into earnings in 2013 12    
Discount rates used in measuring benefit obligations 3.25% 4.25% 4.25%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year 7.50% 8.00%  
Effect on postretirement expense from one-percentage-point increase or decrease in assumed health care trend rate 10.00%    
Effect On Postretirement Benefit Obligation From One Percentage Point Increase Decrease In Assumed Health Care Trend Rate 5.00%    
Health care cost trend rate, year 2018 2018  
Future health care benefit payments in 2012 33    
Future health care benefit payments in 2013 33    
Future health care benefit payments in 2014 32    
Future health care benefit payments in 2015 31    
Future health care benefit payments in 2016 31    
Total future health care benefit payments over the five years 2017 through 2021 $ 138    
Postretirement Plans [Member] | 2018 [Member]
     
Postretirement Benefit Plans [Line Items]      
Ultimate Healthcare Cost Trend Rate 5.00% 5.00%