Guarantor and Non-Guarantor Subsidiaries Financial Information - Consolidating Balance Sheet Unaudited (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017
Current assets:
Cash and equivalents	$ 541		$ 514
Accounts receivable, net	744		447
Inventories	67		42
Royalty advances expected to be recouped within one year	171		123
Prepaid and other current assets	57		50
Total current assets	1,580		1,176
Royalty advances expected to be recouped after one year	209		153
Property, plant and equipment, net	296		229
Goodwill	1,772		1,692
Intangible assets subject to amortization, net	1,780		1,851
Intangible assets not subject to amortization	153		154
Deferred tax assets, net	7		11
Other assets	158		78
Total assets	5,955		5,344
Current liabilities:
Accounts payable	208		281
Accrued royalties	1,577		1,396
Accrued liabilities	448		423
Accrued interest	18		31
Deferred revenue	170		208
Other current liabilities	123		34
Total current liabilities	2,544		2,373
Long-term debt	3,006		2,819
Deferred tax liabilities, net	236		165
Other noncurrent liabilities	302		307
Total liabilities	6,088		5,664
Total Warner Music Group Corp. (deficit) equity	(152)		(334)
Noncontrolling interest	19		14
Total equity	(133)	$ (120)	(320)	$ 191	$ 205	$ 308
Total liabilities and equity	5,955		5,344
Reportable Legal Entities | Guarantor Subsidiaries
Current assets:
Cash and equivalents	297		169
Accounts receivable, net	331		262
Inventories	13		18
Royalty advances expected to be recouped within one year	103		79
Prepaid and other current assets	10		15
Total current assets	754		543
Due from (to) parent companies	(430)		(214)
Investments in and advances to consolidated subsidiaries	2,394		2,192
Royalty advances expected to be recouped after one year	126		93
Property, plant and equipment, net	195		155
Goodwill	1,370		1,370
Intangible assets subject to amortization, net	902		956
Intangible assets not subject to amortization	71		71
Other assets	124		55
Total assets	5,506		5,221
Current liabilities:
Accounts payable	127		200
Accrued royalties	803		869
Accrued liabilities	234		195
Deferred revenue	51		94
Other current liabilities	42		2
Total current liabilities	1,257		1,360
Deferred tax liabilities, net	61		3
Other noncurrent liabilities	182		197
Total liabilities	1,500		1,560
Total Warner Music Group Corp. (deficit) equity	4,002		3,656
Noncontrolling interest	4		5
Total equity	4,006		3,661
Total liabilities and equity	5,506		5,221
Reportable Legal Entities | Non-Guarantor Subsidiaries
Current assets:
Cash and equivalents	244		345
Accounts receivable, net	413		185
Inventories	54		24
Royalty advances expected to be recouped within one year	68		44
Prepaid and other current assets	47		35
Total current assets	826		633
Due from (to) parent companies	(43)		(274)
Royalty advances expected to be recouped after one year	83		60
Property, plant and equipment, net	101		74
Goodwill	402		322
Intangible assets subject to amortization, net	878		895
Intangible assets not subject to amortization	82		83
Deferred tax assets, net	7		11
Other assets	29		11
Total assets	2,365		1,815
Current liabilities:
Accounts payable	81		81
Accrued royalties	769		527
Accrued liabilities	214		228
Deferred revenue	119		114
Other current liabilities	81		32
Total current liabilities	1,264		982
Deferred tax liabilities, net	175		162
Other noncurrent liabilities	110		108
Total liabilities	1,549		1,252
Total Warner Music Group Corp. (deficit) equity	801		554
Noncontrolling interest	15		9
Total equity	816		563
Total liabilities and equity	2,365		1,815
Reportable Legal Entities | Warner Music Group Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	809		675
Total assets	809		675
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	809		675
Total equity	809		675
Total liabilities and equity	809		675
Reportable Legal Entities | WMG Acquisition Corp.
Current assets:
Cash and equivalents	0
Total current assets	0
Due from (to) parent companies	473		488
Investments in and advances to consolidated subsidiaries	2,409		2,018
Other assets	5		12
Total assets	2,887		2,518
Current liabilities:
Accrued royalties	5
Accrued interest	18		31
Total current liabilities	23		31
Long-term debt	3,006		2,819
Other noncurrent liabilities	10		2
Total liabilities	3,039		2,852
Total Warner Music Group Corp. (deficit) equity	(152)		(334)
Total equity	(152)		(334)
Total liabilities and equity	2,887		2,518
Reportable Legal Entities | WMG Acquisition Corp. Consolidated
Current assets:
Cash and equivalents	541		514
Accounts receivable, net	744		447
Inventories	67		42
Royalty advances expected to be recouped within one year	171		123
Prepaid and other current assets	57		50
Total current assets	1,580		1,176
Royalty advances expected to be recouped after one year	209		153
Property, plant and equipment, net	296		229
Goodwill	1,772		1,692
Intangible assets subject to amortization, net	1,780		1,851
Intangible assets not subject to amortization	153		154
Deferred tax assets, net	7		11
Other assets	158		78
Total assets	5,955		5,344
Current liabilities:
Accounts payable	208		281
Accrued royalties	1,577		1,396
Accrued liabilities	448		423
Accrued interest	18		31
Deferred revenue	170		208
Other current liabilities	123		34
Total current liabilities	2,544		2,373
Long-term debt	3,006		2,819
Deferred tax liabilities, net	236		165
Other noncurrent liabilities	302		307
Total liabilities	6,088		5,664
Total Warner Music Group Corp. (deficit) equity	(152)		(334)
Noncontrolling interest	19		14
Total equity	(133)		(320)
Total liabilities and equity	5,955		5,344
Reportable Legal Entities | WMG Holdings Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	809		675
Total assets	809		675
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	809		675
Total equity	809		675
Total liabilities and equity	809		675
Eliminations
Current assets:
Investments in and advances to consolidated subsidiaries	(1,618)		(1,350)
Total assets	(1,618)		(1,350)
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	(1,618)		(1,350)
Total equity	(1,618)		(1,350)
Total liabilities and equity	(1,618)		(1,350)
Eliminations | WMG Acquisition Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	(4,803)		(4,210)
Total assets	(4,803)		(4,210)
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	(4,803)		(4,210)
Total equity	(4,803)		(4,210)
Total liabilities and equity	$ (4,803)		$ (4,210)