Guarantor and Non-Guarantor Subsidiaries Financial Information - Consolidating Statement of Operations Unaudited (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Condensed Income Statements Captions [Line Items]
Revenues		$ 963	$ 825	$ 2,008	$ 1,742
Costs and expenses:
Cost of revenue		(488)	(415)	(1,057)	(911)
Selling, general and administrative expenses	[1]	(337)	(282)	(670)	(558)
Amortization of intangible assets		(55)	(50)	(108)	(101)
Total costs and expenses		(880)	(747)	(1,835)	(1,570)
Operating income		83	78	173	172
Loss on extinguishment of debt		(23)		(24)	(32)
Interest expense, net		(36)	(36)	(72)	(76)
Other income (expense), net		(6)	(19)	(2)
Income before income taxes		18	23	75	64
Income tax expense		(19)	(3)	(71)	(20)
Net income (loss)		(1)	20	4	44
Less: Income attributable to noncontrolling interest		(2)	(1)	(3)	(3)
Net income (loss) attributable to Warner Music Group Corp.		(3)	19	1	41
Reportable Legal Entities | Guarantor Subsidiaries
Condensed Income Statements Captions [Line Items]
Revenues		535	470	1,082	960
Costs and expenses:
Cost of revenue		(242)	(204)	(499)	(424)
Selling, general and administrative expenses		(244)	(199)	(479)	(375)
Amortization of intangible assets		(23)	(26)	(47)	(51)
Total costs and expenses		(509)	(429)	(1,025)	(850)
Operating income		26	41	57	110
Interest expense, net			1	1	2
Equity gains (losses) from equity method investments		33	11	76	51
Other income (expense), net		(1)		9	3
Income before income taxes		58	53	143	166
Income tax expense		(18)	(4)	(69)	(22)
Net income (loss)		40	49	74	144
Less: Income attributable to noncontrolling interest		(1)		(1)
Net income (loss) attributable to Warner Music Group Corp.		39	49	73	144
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Income Statements Captions [Line Items]
Revenues		549	439	1,170	960
Costs and expenses:
Cost of revenue		(327)	(268)	(720)	(609)
Selling, general and administrative expenses		(135)	(110)	(273)	(238)
Amortization of intangible assets		(32)	(24)	(61)	(50)
Total costs and expenses		(494)	(402)	(1,054)	(897)
Operating income		55	37	116	63
Interest expense, net		(5)	(16)	(13)	(34)
Other income (expense), net		(9)	(13)	(11)	(9)
Income before income taxes		41	8	92	20
Income tax expense		(18)	(7)	(28)	(16)
Net income (loss)		23	1	64	4
Less: Income attributable to noncontrolling interest		(1)	(1)	(2)	(3)
Net income (loss) attributable to Warner Music Group Corp.		22		62	1
Reportable Legal Entities | Warner Music Group Corp.
Costs and expenses:
Equity gains (losses) from equity method investments		(3)	19	1	41
Income before income taxes		(3)	19	1	41
Net income (loss)		(3)	19	1	41
Net income (loss) attributable to Warner Music Group Corp.		(3)	19	1	41
Reportable Legal Entities | WMG Acquisition Corp.
Costs and expenses:
Selling, general and administrative expenses					(1)
Total costs and expenses					(1)
Operating income					(1)
Loss on extinguishment of debt		(23)		(24)	(32)
Interest expense, net		(31)	(21)	(60)	(44)
Equity gains (losses) from equity method investments		66	49	156	132
Other income (expense), net		4	(6)		6
Income before income taxes		16	22	72	61
Income tax expense		(19)	(3)	(71)	(20)
Net income (loss)		(3)	19	1	41
Net income (loss) attributable to Warner Music Group Corp.		(3)	19	1	41
Reportable Legal Entities | WMG Acquisition Corp. Consolidated
Condensed Income Statements Captions [Line Items]
Revenues		963	825	2,008	1,742
Costs and expenses:
Cost of revenue		(488)	(415)	(1,057)	(911)
Selling, general and administrative expenses		(337)	(282)	(670)	(558)
Amortization of intangible assets		(55)	(50)	(108)	(101)
Total costs and expenses		(880)	(747)	(1,835)	(1,570)
Operating income		83	78	173	172
Loss on extinguishment of debt		(23)		(24)	(32)
Interest expense, net		(36)	(36)	(72)	(76)
Other income (expense), net		(6)	(19)	(2)
Income before income taxes		18	23	75	64
Income tax expense		(19)	(3)	(71)	(20)
Net income (loss)		(1)	20	4	44
Less: Income attributable to noncontrolling interest		(2)	(1)	(3)	(3)
Net income (loss) attributable to Warner Music Group Corp.		(3)	19	1	41
Reportable Legal Entities | WMG Holdings Corp.
Costs and expenses:
Equity gains (losses) from equity method investments		(3)	19	1	41
Income before income taxes		(3)	19	1	41
Net income (loss)		(3)	19	1	41
Net income (loss) attributable to Warner Music Group Corp.		(3)	19	1	41
Eliminations
Costs and expenses:
Equity gains (losses) from equity method investments		6	(38)	(2)	(82)
Income before income taxes		6	(38)	(2)	(82)
Net income (loss)		6	(38)	(2)	(82)
Net income (loss) attributable to Warner Music Group Corp.		6	(38)	(2)	(82)
Eliminations | WMG Acquisition Corp.
Condensed Income Statements Captions [Line Items]
Revenues		(121)	(84)	(244)	(178)
Costs and expenses:
Cost of revenue		81	57	162	122
Selling, general and administrative expenses		42	27	82	56
Total costs and expenses		123	84	244	178
Operating income		2
Equity gains (losses) from equity method investments		(99)	(60)	(232)	(183)
Income before income taxes		(97)	(60)	(232)	(183)
Income tax expense		36	11	97	38
Net income (loss)		(61)	(49)	(135)	(145)
Net income (loss) attributable to Warner Music Group Corp.		$ (61)	$ (49)	$ (135)	$ (145)

[1] (a) Includes depreciation expense of: $(14) $(13) $(26) $(25)