Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Information [Line Items]
Sales	$ 594	$ 577	$ 569	$ 545	$ 547	$ 534	$ 514	$ 489	$ 2,285	$ 2,084	$ 1,929
Gross profit	203	201	207	195	196	197	198	185	806	776	748
Operating income (loss)	105	102	100	88	113	87	100	94	395	394	396
Income before income taxes	57	97	94	84	177	94	109	110	332	490	421
Net income	$ 45	$ 64	$ 67	$ (10)	$ 105	$ 56	$ 71	$ 72	$ 166	$ 304	$ 273
Net (loss) income per common share, basic (usd per share)	$ 0.23	$ 0.33	$ 0.33	$ (0.05)	$ 0.52	$ 0.27	$ 0.35	$ 0.35	$ 0.84	$ 1.49	$ 1.60
Net (loss) income per common share, diluted (usd per share)	$ 0.23	$ 0.33	$ 0.33	$ (0.05)	$ 0.52	$ 0.27	$ 0.35	$ 0.35	$ 0.84	$ 1.49	$ 1.60
Pension and other postretirement benefit plan remeasurement gains (losses)	$ (38)				$ 60			$ 8	$ 0	$ 138	$ 35
Income tax expense	$ 2	$ 3	$ 2	$ 71					$ 166	$ 186	$ 148
Legacy And Separation-Related Expenses, Net
Quarterly Financial Information [Line Items]
Operating income (loss)		$ 3	$ (8)	$ (9)	$ (14)	$ (13)	$ (6)	$ (6)