Stockholders' Deficit - Schedule of Share Repurchases (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Total cost	$ 325	$ 50	$ 0
Shares repurchased (in shares)	15	2	0

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration