Shareholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	$ (825)	$ (760)	$ (809)	$ (766)
Other comprehensive income (loss) before reclassification	20	9	(6)	6
Amounts reclassified from accumulated other comprehensive loss	11	9	21	18
Net current-period other comprehensive income (loss)	31	18	15	24
Ending balance	(794)	(742)	(794)	(742)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(94)	(60)	(66)	(54)
Other comprehensive income (loss) before reclassification	19	10	(9)	4
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net current-period other comprehensive income (loss)	19	10	(9)	4
Ending balance	(75)	(50)	(75)	(50)
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(729)	(696)	(740)	(705)
Other comprehensive income (loss) before reclassification	0	0	1	0
Amounts reclassified from accumulated other comprehensive loss	11	9	21	18
Net current-period other comprehensive income (loss)	11	9	22	18
Ending balance	(718)	(687)	(718)	(687)
Unrealized Loss, net of tax
Accumulated Other Comprehensive Income (Loss), Net Of Tax [Roll Forward]
Beginning balance	(2)	(4)	(3)	(7)
Other comprehensive income (loss) before reclassification	1	(1)	2	2
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net current-period other comprehensive income (loss)	1	(1)	2	2
Ending balance	$ (1)	$ (5)	$ (1)	$ (5)