Employee Benefit Plans - Pension and Other Postretirement Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost (income)	$ (25)
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	$ 2
Interest cost	21	6
Expected return on plan assets	(36)	(9)
Amortization of prior service credit	0	0
Actuarial gain	0	0
Net periodic benefit cost (income)	(14)	(1)
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	0	0
Expected return on plan assets	0	0
Amortization of prior service credit	(3)	0
Actuarial gain	(8)	0
Net periodic benefit cost (income)	$ (11)	$ 0