Shareholders' Equity - Reclassifications from AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	$ 10	$ 9
Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	10	9
Amount Reclassified from Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the period	10
Amount Reclassified from Accumulated Other Comprehensive Income | Employee Benefit Related Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Prior service costs	(1)
Amount Reclassified from Accumulated Other Comprehensive Income | Actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	11	9
Amount Reclassified from Accumulated Other Comprehensive Income | Employee Benefit Related Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total before tax	10	9
Tax expense	$ 0	0
Total reclassifications for the period		$ 9