Pension Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Net Periodic Benefit Cost Abstract
Interest cost	$ 9	$ 8	$ 19	$ 17
Expected return on plan assets	(10)	(10)	(20)	(20)
Recognized actuarial loss	2	2	3	4
Net periodic benefit cost	$ 1	$ 0	$ 2	$ 1