Guarantor and Non-Guarantor Subsidiaries Financial Information - Consolidating Statement of Comprehensive Income Unaudited (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	$ 67	$ (1)	$ 153	$ 4
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	(10)	9	(26)	18
Deferred (loss) gain on derivative	(3)	1	(9)	2
Other comprehensive (loss) income, net of tax	(13)	10	(35)	20
Total comprehensive income	54	9	118	24
Less: Income attributable to noncontrolling interest		(2)		(3)
Comprehensive income attributable to Warner Music Group Corp.	54	7	118	21
Reportable Legal Entities | Guarantor Subsidiaries
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	73	40	201	74
Other comprehensive (loss) income, net of tax:
Total comprehensive income	73	40	201	74
Less: Income attributable to noncontrolling interest		(1)		(1)
Comprehensive income attributable to Warner Music Group Corp.	73	39	201	73
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	15	23	99	64
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	10	(9)	26	(18)
Deferred (loss) gain on derivative		1	(2)
Other comprehensive (loss) income, net of tax	10	(8)	24	(18)
Total comprehensive income	25	15	123	46
Less: Income attributable to noncontrolling interest		(1)		(2)
Comprehensive income attributable to Warner Music Group Corp.	25	14	123	44
Reportable Legal Entities | Warner Music Group Corp.
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	67	(3)	153	1
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	(13)	9	(29)	18
Deferred (loss) gain on derivative	(3)	1	(9)	2
Other comprehensive (loss) income, net of tax	(16)	10	(38)	20
Total comprehensive income	51	7	115	21
Comprehensive income attributable to Warner Music Group Corp.	51	7	115	21
Reportable Legal Entities | WMG Acquisition Corp.
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	67	(3)	153	1
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	(10)	9	(26)	18
Deferred (loss) gain on derivative	(3)	1	(9)	2
Other comprehensive (loss) income, net of tax	(13)	10	(35)	20
Total comprehensive income	54	7	118	21
Comprehensive income attributable to Warner Music Group Corp.	54	7	118	21
Reportable Legal Entities | WMG Acquisition Corp. Consolidated
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	67	(1)	153	4
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	(10)	9	(26)	18
Deferred (loss) gain on derivative	(3)	1	(9)	2
Other comprehensive (loss) income, net of tax	(13)	10	(35)	20
Total comprehensive income	54	9	118	24
Less: Income attributable to noncontrolling interest		(2)		(3)
Comprehensive income attributable to Warner Music Group Corp.	54	7	118	21
Reportable Legal Entities | WMG Holdings Corp.
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	67	(3)	153	1
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	(13)	9	(29)	18
Deferred (loss) gain on derivative	(3)	1	(9)	2
Other comprehensive (loss) income, net of tax	(16)	10	(38)	20
Total comprehensive income	51	7	115	21
Comprehensive income attributable to Warner Music Group Corp.	51	7	115	21
Eliminations
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	(134)	6	(306)	(2)
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	26	(18)	58	(36)
Deferred (loss) gain on derivative	6	(2)	18	(4)
Other comprehensive (loss) income, net of tax	32	(20)	76	(40)
Total comprehensive income	(102)	(14)	(230)	(42)
Comprehensive income attributable to Warner Music Group Corp.	(102)	(14)	(230)	(42)
Eliminations | WMG Acquisition Corp.
Condensed Statement Of Income Captions [Line Items]
Net income (loss)	(88)	(61)	(300)	(135)
Other comprehensive (loss) income, net of tax:
Foreign currency adjustment	(10)	9	(26)	18
Deferred (loss) gain on derivative		(1)	2
Other comprehensive (loss) income, net of tax	(10)	8	(24)	18
Total comprehensive income	(98)	(53)	(324)	(117)
Comprehensive income attributable to Warner Music Group Corp.	$ (98)	$ (53)	$ (324)	$ (117)