Guarantor and Non-Guarantor Subsidiaries Financial Information - Consolidating Statement of Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Condensed Statement Of Income Captions [Line Items]
Net income	$ 312	$ 149	$ 30
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	(13)	30	(44)
Minimum pension liability	1	7	(7)
Deferred (loss) gain on derivative financial instruments	3
Other comprehensive (loss) income, net of tax	(9)	37	(51)
Total comprehensive income (loss)	303	186	(21)
Less: Income attributable to noncontrolling interest	(5)	(6)	(5)
Comprehensive income (loss) attributable to Warner Music Group Corp.	298	180	(26)
Reportable Legal Entities | Guarantor Subsidiaries
Condensed Statement Of Income Captions [Line Items]
Net income	61	282	167
Other comprehensive income (loss), net of tax:
Deferred (loss) gain on derivative financial instruments		(1)	(1)
Other comprehensive (loss) income, net of tax		(1)	(1)
Total comprehensive income (loss)	61	281	166
Less: Income attributable to noncontrolling interest	(1)	(1)	(1)
Comprehensive income (loss) attributable to Warner Music Group Corp.	60	280	165
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Statement Of Income Captions [Line Items]
Net income	104	59	54
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	13	(30)	(44)
Minimum pension liability	1	7	(7)
Deferred (loss) gain on derivative financial instruments	3
Other comprehensive (loss) income, net of tax	17	(23)	(51)
Total comprehensive income (loss)	121	36	3
Less: Income attributable to noncontrolling interest	(4)	(5)	(4)
Comprehensive income (loss) attributable to Warner Music Group Corp.	117	31	(1)
Reportable Legal Entities | Warner Music Group Corp.
Condensed Statement Of Income Captions [Line Items]
Net income	307	143	25
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	(13)	32	(44)
Minimum pension liability	1	7	(7)
Deferred (loss) gain on derivative financial instruments	3
Other comprehensive (loss) income, net of tax	(9)	39	(51)
Total comprehensive income (loss)	298	182	(26)
Comprehensive income (loss) attributable to Warner Music Group Corp.	298	182	(26)
Reportable Legal Entities | WMG Acquisition Corp.
Condensed Statement Of Income Captions [Line Items]
Net income	307	143	53
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	(13)	30	(44)
Minimum pension liability	1	7	(7)
Deferred (loss) gain on derivative financial instruments	3
Other comprehensive (loss) income, net of tax	(9)	37	(51)
Total comprehensive income (loss)	298	180	2
Comprehensive income (loss) attributable to Warner Music Group Corp.	298	180	2
Reportable Legal Entities | WMG Acquisition Corp. Consolidated
Condensed Statement Of Income Captions [Line Items]
Net income	312	149	58
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	(13)	30	(44)
Minimum pension liability	1	7	(7)
Deferred (loss) gain on derivative financial instruments	3
Other comprehensive (loss) income, net of tax	(9)	37	(51)
Total comprehensive income (loss)	303	186	7
Less: Income attributable to noncontrolling interest	(5)	(6)	(5)
Comprehensive income (loss) attributable to Warner Music Group Corp.	298	180	2
Reportable Legal Entities | WMG Holdings Corp.
Condensed Statement Of Income Captions [Line Items]
Net income	307	143	25
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	(13)	32	(44)
Minimum pension liability	1	7	(7)
Deferred (loss) gain on derivative financial instruments	3
Other comprehensive (loss) income, net of tax	(9)	39	(51)
Total comprehensive income (loss)	298	182	(26)
Comprehensive income (loss) attributable to Warner Music Group Corp.	298	182	(26)
Eliminations
Condensed Statement Of Income Captions [Line Items]
Net income	(614)	(286)	(78)
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	26	(64)	88
Minimum pension liability	(2)	(14)	14
Deferred (loss) gain on derivative financial instruments	(6)
Other comprehensive (loss) income, net of tax	18	(78)	102
Total comprehensive income (loss)	(596)	(364)	24
Comprehensive income (loss) attributable to Warner Music Group Corp.	(596)	(364)	24
Eliminations | WMG Acquisition Corp.
Condensed Statement Of Income Captions [Line Items]
Net income	(160)	(335)	(216)
Other comprehensive income (loss), net of tax:
Foreign currency adjustment	(13)	30	44
Minimum pension liability	(1)	(7)	7
Deferred (loss) gain on derivative financial instruments	(3)	1	1
Other comprehensive (loss) income, net of tax	(17)	24	52
Total comprehensive income (loss)	(177)	(311)	(164)
Comprehensive income (loss) attributable to Warner Music Group Corp.	$ (177)	$ (311)	$ (164)