Equity and Noncontrolling Interests - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended
	Mar. 31, 2019		Dec. 31, 2018	Mar. 31, 2018		Mar. 31, 2019		Mar. 31, 2018		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	$ 2		$ (12)	$ 1		$ 2		$ 1			$ 7
Foreign currency translation adjustments
Balance at beginning of period	(1,066)			(423)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent	114			168
Balance at end of period	(952)		(1,066)	(255)		(952)		(255)
Realized and unrealized gains (losses) on derivatives
Current period changes in fair value	17			(10)		19		(11)
Realized and unrealized gains (losses) on marketable securities
Balance at beginning of period	0			4
Current period changes in fair value	0			(2)
Balance at end of period	0		0	2		0		2
Reclassification to income, tax effect						0
Pension and postretirement plans
Balance at beginning of period	(2)			(2)
Other changes	0			0
Balance at end of period	(2)		(2)	(2)		(2)		(2)
Accumulated other comprehensive loss	(952)			(254)		(952)		(254)		$ (946)
Foreign currency translation adjustments
Foreign currency translation adjustments
Balance at beginning of period			(939)			(939)		(481)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent						(13)		226
Balance at end of period	(952)			(255)		(952)		(255)
Aggregate adjustment for period, tax effect	0	[1]		0	[1]	0		1
Realized and unrealized gains (losses) on derivatives
Realized and unrealized gains (losses) on derivatives
Current period changes in fair value	12			(4)		8		2
Reclassification to income	2			(2)		7		(7)
Current period changes in fair value, tax effect	6			(2)		4		1
Reclassifcation to income, tax effect	2	[2]		0	[2]	3	[1]	(2)	[1]
Realized and unrealized gains (losses) on marketable securities
Realized and unrealized gains (losses) on marketable securities
Balance at beginning of period			8			8		4
Current period changes in fair value						0		(2)
Balance at end of period	0			2		0		2
Current period changes in fair value, tax effect						0		0
Pension and postretirement plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax						0		0
Pension and postretirement plans
Balance at beginning of period			(2)			(2)		(2)
Balance at end of period	(2)			(2)		(2)		(2)
Scott Safety business [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax								12
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax						0
Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest [Member] | Realized and unrealized gains (losses) on derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	$ 2			$ 1		2		1		$ (13)		$ 6
Retained Earnings | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax			$ 8			8
AOCI Attributable to Parent [Member] | Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax						$ (8)		$ 0

[1] * During the six months ended March 31, 2018, $12 million of cumulative CTA was recognized as part of the divestiture-related gain recognized as part of the divestiture of Scott Safety.

[2] ** Refer to Note 15, "Derivative Instruments and Hedging Activities," of the notes to consolidated financial statements for disclosure of the line items in the consolidated statements of income affected by reclassifications from AOCI into income related to derivatives.
*** As previously disclosed, during the quarter ended December 31, 2018, the Company adopted ASU 2016-01, "Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities." As a result the Company reclassified $8 million of unrealized gains on marketable securities to retained earnings as of October 1, 2018.