Stock-Based Compensation Plans - Schedule of SARs Activity (Details) - Stock appreciation rights - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
SARs outstanding at beginning of period (in shares)	1,798
Granted (in shares)	240
Exercised (in shares)	(185)
Forfeited (in shares)	(38)
SARs outstanding at end of period (in shares)	1,815	1,798
SARs exercisable at end of period (in shares)	1,342
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
SARs outstanding at beginning of period, weighted average exercise price per share (USD per share)	$ 18.54
Granted, weighted average exercise price per share (USD per share)	20.37
Exercised, weighted average exercise price per share (USD per share)	17.19
Forfeited, weighted average exercise price per share (USD per share)	20.35
SARs outstanding at end of period, weighted average exercise price per share (USD per share)	18.88	$ 18.54
SARs exercisable at end of period, weighted average exercise price per share (USD per share)	$ 18.15
Outstanding, weighted average remaining term	6 years 2 months 12 days	6 years 8 months 12 days
Exercisable, weighted average remaining term	5 years 4 months 24 days
Outstanding, aggregate intrinsic value	$ 6	$ 6
Exercised, aggregate intrinsic value	1
Exercisable, aggregate intrinsic value	$ 5