Employee Benefit Plans - Schedule of Future Benefit Payments (Details) $ in Millions	Sep. 30, 2018 USD ($)
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
2019	$ 142
2020	142
2021	143
2022	142
2023	141
Thereafter	695
Total	1,405
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
2019	6
2020	5
2021	4
2022	4
2023	3
Thereafter	15
Total	$ 37