Shareholders' Equity - Reclassifications from AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	$ 11	$ 9	$ 32	$ 27
Amount Reclassified from Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	8
Amount Reclassified from Accumulated Other Comprehensive Income | Prior service costs
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service costs	(1)		(2)
Amount Reclassified from Accumulated Other Comprehensive Income | Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	12	9	34	27
Amount Reclassified from Accumulated Other Comprehensive Income | Employee Benefit Related Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	11	9	32	27
Tax expense (benefit)	$ (3)	0	(10)	0
Total reclassifications for the period		$ 9	$ 22	$ 27