Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Quarterly Financial Information [Line Items]
Sales	$ 629	$ 613	$ 591	$ 557	$ 594	$ 577	$ 569	$ 545	$ 2,390	$ 2,285	$ 2,084
Gross profit	217	207	203	183	203	201	207	195	810	806	776
Operating income (loss)	113	102	96	87	105	102	100	88	398	395	394
Income before income taxes	28	85	80	72	57	97	94	84	265	332	490
Net income (loss)	$ 27	$ 65	$ 63	$ 53	$ 45	$ 64	$ 67	$ (10)	$ 208	$ 166	$ 304
Net income (loss) per common share, basic (usd per share)	$ 0.14	$ 0.34	$ 0.33	$ 0.28	$ 0.23	$ 0.33	$ 0.33	$ (0.05)	$ 1.10	$ 0.84	$ 1.49
Net income (loss) per common share, diluted (usd per share)	$ 0.14	$ 0.34	$ 0.33	$ 0.28	$ 0.23	$ 0.33	$ 0.33	$ (0.05)	$ 1.10	$ 0.84	$ 1.49
Pension and other postretirement benefit plan remeasurement losses	$ 69				$ 38				$ (60)	$ 0	$ 138
Income tax expense (benefit)			$ (2)		2	$ 3	$ 2	$ 71	$ 57	$ 166	$ 186
Cost of Sales
Quarterly Financial Information [Line Items]
Gross profit		$ 5	1
Selling, General and Administrative Expenses
Quarterly Financial Information [Line Items]
Operating income (loss)	2	$ 4	8		$ 1	2
Legacy And Separation-Related Expenses, Net
Quarterly Financial Information [Line Items]
Operating income (loss)			$ 3			$ 3	$ 8	$ 9
Other Operating Income (Expense)
Quarterly Financial Information [Line Items]
Operating income (loss)	$ 4