Accumulated Other Comprehensive Loss (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2016
Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Accumulated other comprehensive loss $ (1,693) $ (1,373) $ (1,699) $ (1,366)
Other comprehensive income (loss) before reclassifications 8 (22) (1) (41)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax (15) (13) (30) (25)
Net current period other comprehensive income (loss) 23 (9) 29 (16)
Accumulated other comprehensive loss (1,670) (1,382) (1,670) (1,382)
Foreign Exchange Translation Adjustment [Member]        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Accumulated other comprehensive loss (64) (29) (56) (15)
Other comprehensive income (loss) before reclassifications 8 (22) 0 (36)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax 0 0 0 0
Net current period other comprehensive income (loss) 8 (22) 0 (36)
Accumulated other comprehensive loss (56) (51) (56) (51)
Pension and Other Postretirement Adjustments [Member]        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Accumulated other comprehensive loss [1] (1,624) (1,337) (1,637) (1,348)
Other comprehensive income (loss) before reclassifications [1] 0 0 0 0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [1] (13) (12) (26) (23)
Net current period other comprehensive income (loss) [1] 13 12 26 23
Accumulated other comprehensive loss [1] (1,611) (1,325) (1,611) (1,325)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax 21 18 42 36
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax 13 12 26 23
Change in the Fair Value of Effective Cash Flow Hedges [Member]        
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]        
Accumulated other comprehensive loss (5) (7) (6) (3)
Other comprehensive income (loss) before reclassifications 0 0 (1) (5)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax (2) (1) (4) (2)
Net current period other comprehensive income (loss) 2 1 3 (3)
Accumulated other comprehensive loss $ (3) $ (6) $ (3) $ (6)
[1] Reclassifications from AOCL to net income, related to the amortization of net actuarial losses and prior service credits for the Company's retirement benefit plans, were $21 million ($13 million net of tax) and $18 million ($12 million net of tax) for the three months ended March 31, 2016 and 2015, respectively, and were $42 million ($26 million net of tax) and $36 million ($23 million net of tax) for the six months ended March 31, 2016 and 2015, respectively. The reclassifications are included in the computation of net benefit expense. See Note 9, Retirement Benefits, for additional details.