Consolidated Statements of Deficit (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (285)	$ (120)	$ (269)	$ (320)	$ (320)
Net (loss) income	(519)	14	(471)	167
Other comprehensive income (loss), net of tax	15	6	(13)	(29)
Dividends ($— per share)		(31)	(75)	(94)
Distribution to noncontrolling interest holders	(5)	(1)	(6)	(3)
Modification of stock-based compensation plan	769		769
Stock-based compensation expense	3		3
Shares listed through IPO	0		0
Other	1	(1)	1	(4)
Ending balance	(21)	$ (133)	(21)	(133)	$ (269)	$ (320)
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201609Member	us-gaap:AccountingStandardsUpdate201409Member
Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 0			$ 150	$ 150
Ending balance						$ 150
ASC 842 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			7
Ending balance					7
ASC 718 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 33
Ending balance					$ 33
Class A Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)			0
Ending balance (in shares)	77,000,000		77,000,000		0
Class B Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)			505,830,022
Ending balance (in shares)	433,000,000		433,000,000		505,830,022
Common Stock | Class A Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	0	0	0	0	0
Beginning balance	$ 0	$ 0	$ 0	$ 0	$ 0
Shares listed through IPO (in shares)	77,000,000		77,000,000
Ending balance (in shares)	77,000,000	0	77,000,000	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Common Stock | Class B Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	510,000,000	505,830,022	505,830,022	501,991,944	501,991,944
Beginning balance	$ 1	$ 1	$ 1	$ 1	$ 1
Shares listed through IPO (in shares)	(77,000,000)		(77,000,000)
Other (in shares)			4,169,978	3,838,078
Ending balance (in shares)	433,000,000	505,830,022	433,000,000	505,830,022	505,830,022	501,991,944
Ending balance	$ 1	$ 1	$ 1	$ 1	$ 1	$ 1
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,127	1,127	1,127	1,127	1,127
Modification of stock-based compensation plan	769		769
Stock-based compensation expense	3		3
Ending balance	1,899	1,127	1,899	1,127	1,127	1,127
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,166)	(1,043)	(1,177)	(1,272)	(1,272)
Net (loss) income	(520)	13	(474)	166
Dividends ($— per share)		(31)	(75)	(94)
Other	(1)		(1)
Ending balance	(1,685)	(1,061)	(1,685)	(1,061)	(1,177)	(1,272)
Accumulated Deficit | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0			139	139
Ending balance						139
Accumulated Deficit | ASC 842 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			7
Ending balance					7
Accumulated Deficit | ASC 718 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			33
Ending balance	33		33		33
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(268)	(225)	(240)	(190)	(190)
Other comprehensive income (loss), net of tax	15	6	(13)	(29)
Ending balance	(253)	(219)	(253)	(219)	(240)	(190)
Total Warner Music Group Corp. Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(306)	(140)	(289)	(334)	(334)
Net (loss) income	(520)	13	(474)	166
Other comprehensive income (loss), net of tax	15	6	(13)	(29)
Dividends ($— per share)		(31)	(75)	(94)
Modification of stock-based compensation plan	769		769
Stock-based compensation expense	3		3
Other	(1)		(1)
Ending balance	(38)	(152)	(38)	(152)	(289)	(334)
Total Warner Music Group Corp. Deficit | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0			139	139
Ending balance						139
Total Warner Music Group Corp. Deficit | ASC 842 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			7
Ending balance					7
Total Warner Music Group Corp. Deficit | ASC 718 | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			33
Ending balance					33
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	21	20	20	14	14
Net (loss) income	1	1	3	1
Distribution to noncontrolling interest holders	(5)	(1)	(6)	(3)
Other	0	(1)		(4)
Ending balance	$ 17	$ 19	$ 17	19	20	14
Noncontrolling Interest | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance				$ 11	$ 11
Ending balance						$ 11