Income Taxes - Schedule of Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Current
Federal						$ 10	$ (2)	$ 47
State						5	6	8
Non-U.S.						19	17	14
Current income tax expense						34	21	69
Deferred
Federal						24	136	106
State						0	9	12
Non-U.S.						(1)	0	(1)
Deferred income tax expense						23	145	117
Income tax expense	$ (2)	$ 2	$ 3	$ 2	$ 71	$ 57	$ 166	$ 186