Guarantor and Non-Guarantor Subsidiaries Financial Information - Consolidating Statement of Operations Unaudited (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Condensed Income Statements Captions [Line Items]
Revenue		$ 1,090	$ 963	$ 2,293	$ 2,008
Costs and expenses:
Cost of revenue		(559)	(488)	(1,185)	(1,057)
Selling, general and administrative expenses	[1]	(354)	(337)	(730)	(670)
Amortization of intangible assets		(55)	(55)	(109)	(108)
Total costs and expenses		(968)	(880)	(2,024)	(1,835)
Operating income		122	83	269	173
Loss on extinguishment of debt			(23)	(3)	(24)
Interest (expense) income, net		(36)	(36)	(72)	(72)
Other income (expense), net		29	(6)	57	(2)
Income before income taxes		115	18	251	75
Income tax expense		(48)	(19)	(98)	(71)
Net income (loss)		67	(1)	153	4
Less: Income attributable to noncontrolling interest			(2)		(3)
Net income (loss) attributable to Warner Music Group Corp.		67	(3)	153	1
Reportable Legal Entities | Guarantor Subsidiaries
Condensed Income Statements Captions [Line Items]
Revenue		461	535	942	1,082
Costs and expenses:
Cost of revenue		(214)	(242)	(437)	(499)
Selling, general and administrative expenses		(186)	(244)	(375)	(479)
Amortization of intangible assets		(25)	(23)	(50)	(47)
Total costs and expenses		(425)	(509)	(862)	(1,025)
Operating income		36	26	80	57
Interest (expense) income, net		1		2	1
Equity gains (losses) from equity method investments		34	33	143	76
Other income (expense), net		51	(1)	70	9
Income before income taxes		122	58	295	143
Income tax expense		(49)	(18)	(94)	(69)
Net income (loss)		73	40	201	74
Less: Income attributable to noncontrolling interest			(1)		(1)
Net income (loss) attributable to Warner Music Group Corp.		73	39	201	73
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Income Statements Captions [Line Items]
Revenue		672	549	1,526	1,170
Costs and expenses:
Cost of revenue		(391)	(327)	(896)	(720)
Selling, general and administrative expenses		(166)	(135)	(383)	(273)
Amortization of intangible assets		(30)	(32)	(59)	(61)
Total costs and expenses		(587)	(494)	(1,338)	(1,054)
Operating income		85	55	188	116
Interest (expense) income, net		(6)	(5)	(12)	(13)
Other income (expense), net		(38)	(9)	(27)	(11)
Income before income taxes		41	41	149	92
Income tax expense		(26)	(18)	(50)	(28)
Net income (loss)		15	23	99	64
Less: Income attributable to noncontrolling interest			(1)		(2)
Net income (loss) attributable to Warner Music Group Corp.		15	22	99	62
Reportable Legal Entities | Warner Music Group Corp.
Costs and expenses:
Equity gains (losses) from equity method investments		67	(3)	153	1
Income before income taxes		67	(3)	153	1
Net income (loss)		67	(3)	153	1
Net income (loss) attributable to Warner Music Group Corp.		67	(3)	153	1
Reportable Legal Entities | WMG Acquisition Corp.
Costs and expenses:
Loss on extinguishment of debt			(23)	(3)	(24)
Interest (expense) income, net		(31)	(31)	(62)	(60)
Equity gains (losses) from equity method investments		130	66	302	156
Other income (expense), net		16	4	14
Income before income taxes		115	16	251	72
Income tax expense		(48)	(19)	(98)	(71)
Net income (loss)		67	(3)	153	1
Net income (loss) attributable to Warner Music Group Corp.		67	(3)	153	1
Reportable Legal Entities | WMG Acquisition Corp. Consolidated
Condensed Income Statements Captions [Line Items]
Revenue		1,090	963	2,293	2,008
Costs and expenses:
Cost of revenue		(559)	(488)	(1,185)	(1,057)
Selling, general and administrative expenses		(354)	(337)	(730)	(670)
Amortization of intangible assets		(55)	(55)	(109)	(108)
Total costs and expenses		(968)	(880)	(2,024)	(1,835)
Operating income		122	83	269	173
Loss on extinguishment of debt			(23)	(3)	(24)
Interest (expense) income, net		(36)	(36)	(72)	(72)
Other income (expense), net		29	(6)	57	(2)
Income before income taxes		115	18	251	75
Income tax expense		(48)	(19)	(98)	(71)
Net income (loss)		67	(1)	153	4
Less: Income attributable to noncontrolling interest			(2)		(3)
Net income (loss) attributable to Warner Music Group Corp.		67	(3)	153	1
Reportable Legal Entities | WMG Holdings Corp.
Costs and expenses:
Equity gains (losses) from equity method investments		67	(3)	153	1
Income before income taxes		67	(3)	153	1
Net income (loss)		67	(3)	153	1
Net income (loss) attributable to Warner Music Group Corp.		67	(3)	153	1
Eliminations
Costs and expenses:
Equity gains (losses) from equity method investments		(134)	6	(306)	(2)
Income before income taxes		(134)	6	(306)	(2)
Net income (loss)		(134)	6	(306)	(2)
Net income (loss) attributable to Warner Music Group Corp.		(134)	6	(306)	(2)
Eliminations | WMG Acquisition Corp.
Condensed Income Statements Captions [Line Items]
Revenue		(43)	(121)	(175)	(244)
Costs and expenses:
Cost of revenue		46	81	148	162
Selling, general and administrative expenses		(2)	42	28	82
Total costs and expenses		44	123	176	244
Operating income		1	2	1
Equity gains (losses) from equity method investments		(164)	(99)	(445)	(232)
Income before income taxes		(163)	(97)	(444)	(232)
Income tax expense		75	36	144	97
Net income (loss)		(88)	(61)	(300)	(135)
Net income (loss) attributable to Warner Music Group Corp.		$ (88)	$ (61)	$ (300)	$ (135)

[1] (a) Includes depreciation expense of: