Guarantor and Non-Guarantor Subsidiaries Financial Information - Consolidating Balance Sheet Unaudited (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Current assets:
Cash and equivalents	$ 470		$ 514
Accounts receivable, net	781		447
Inventories	65		42
Royalty advances expected to be recouped within one year	151		123
Prepaid and other current assets	57		50
Total current assets	1,524		1,176
Royalty advances expected to be recouped after one year	184		153
Property, plant and equipment, net	295		229
Goodwill	1,787		1,692
Intangible assets subject to amortization, net	1,802		1,851
Intangible assets not subject to amortization	153		154
Deferred tax assets, net	7		11
Other assets	150		78
Total assets	5,902		5,344
Current liabilities:
Accounts payable	245		281
Accrued royalties	1,509		1,396
Accrued liabilities	409		423
Accrued interest	32		31
Deferred revenue	170		208
Other current liabilities	153		34
Total current liabilities	2,518		2,373
Long-term debt	2,990		2,819
Deferred tax liabilities, net	230		165
Other noncurrent liabilities	284		307
Total liabilities	6,022		5,664
Total Warner Music Group Corp. (deficit) equity	(140)		(334)
Noncontrolling interest	20		14
Total equity	(120)	$ (139)	(320)	$ 205	$ 321	$ 308
Total liabilities and equity	5,902		5,344
Reportable Legal Entities | Guarantor Subsidiaries
Current assets:
Cash and equivalents	252		169
Accounts receivable, net	358		262
Inventories	13		18
Royalty advances expected to be recouped within one year	95		79
Prepaid and other current assets	14		15
Total current assets	732		543
Due from (to) parent companies	(385)		(214)
Investments in and advances to consolidated subsidiaries	2,283		2,192
Royalty advances expected to be recouped after one year	115		93
Property, plant and equipment, net	197		155
Goodwill	1,370		1,370
Intangible assets subject to amortization, net	918		956
Intangible assets not subject to amortization	71		71
Other assets	115		55
Total assets	5,416		5,221
Current liabilities:
Accounts payable	168		200
Accrued royalties	792		869
Accrued liabilities	218		195
Deferred revenue	54		94
Other current liabilities	44		2
Total current liabilities	1,276		1,360
Deferred tax liabilities, net	49		3
Other noncurrent liabilities	169		197
Total liabilities	1,494		1,560
Total Warner Music Group Corp. (deficit) equity	3,918		3,656
Noncontrolling interest	4		5
Total equity	3,922		3,661
Total liabilities and equity	5,416		5,221
Reportable Legal Entities | Non-Guarantor Subsidiaries
Current assets:
Cash and equivalents	210		345
Accounts receivable, net	423		185
Inventories	52		24
Royalty advances expected to be recouped within one year	56		44
Prepaid and other current assets	43		35
Total current assets	784		633
Due from (to) parent companies	(95)		(274)
Royalty advances expected to be recouped after one year	69		60
Property, plant and equipment, net	98		74
Goodwill	417		322
Intangible assets subject to amortization, net	884		895
Intangible assets not subject to amortization	82		83
Deferred tax assets, net	7		11
Other assets	29		11
Total assets	2,275		1,815
Current liabilities:
Accounts payable	77		81
Accrued royalties	711		527
Accrued liabilities	191		228
Deferred revenue	116		114
Other current liabilities	109		32
Total current liabilities	1,204		982
Deferred tax liabilities, net	181		162
Other noncurrent liabilities	108		108
Total liabilities	1,493		1,252
Total Warner Music Group Corp. (deficit) equity	766		554
Noncontrolling interest	16		9
Total equity	782		563
Total liabilities and equity	2,275		1,815
Reportable Legal Entities | Warner Music Group Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	790		675
Total assets	790		675
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	790		675
Total equity	790		675
Total liabilities and equity	790		675
Reportable Legal Entities | WMG Acquisition Corp.
Current assets:
Cash and equivalents	8
Total current assets	8
Due from (to) parent companies	480		488
Investments in and advances to consolidated subsidiaries	2,401		2,018
Other assets	6		12
Total assets	2,895		2,518
Current liabilities:
Accrued royalties	6
Accrued interest	32		31
Total current liabilities	38		31
Long-term debt	2,990		2,819
Other noncurrent liabilities	7		2
Total liabilities	3,035		2,852
Total Warner Music Group Corp. (deficit) equity	(140)		(334)
Total equity	(140)		(334)
Total liabilities and equity	2,895		2,518
Reportable Legal Entities | WMG Acquisition Corp. Consolidated
Current assets:
Cash and equivalents	470		514
Accounts receivable, net	781		447
Inventories	65		42
Royalty advances expected to be recouped within one year	151		123
Prepaid and other current assets	57		50
Total current assets	1,524		1,176
Royalty advances expected to be recouped after one year	184		153
Property, plant and equipment, net	295		229
Goodwill	1,787		1,692
Intangible assets subject to amortization, net	1,802		1,851
Intangible assets not subject to amortization	153		154
Deferred tax assets, net	7		11
Other assets	150		78
Total assets	5,902		5,344
Current liabilities:
Accounts payable	245		281
Accrued royalties	1,509		1,396
Accrued liabilities	409		423
Accrued interest	32		31
Deferred revenue	170		208
Other current liabilities	153		34
Total current liabilities	2,518		2,373
Long-term debt	2,990		2,819
Deferred tax liabilities, net	230		165
Other noncurrent liabilities	284		307
Total liabilities	6,022		5,664
Total Warner Music Group Corp. (deficit) equity	(140)		(334)
Noncontrolling interest	20		14
Total equity	(120)		(320)
Total liabilities and equity	5,902		5,344
Reportable Legal Entities | WMG Holdings Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	790		675
Total assets	790		675
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	790		675
Total equity	790		675
Total liabilities and equity	790		675
Eliminations
Current assets:
Investments in and advances to consolidated subsidiaries	(1,580)		(1,350)
Total assets	(1,580)		(1,350)
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	(1,580)		(1,350)
Total equity	(1,580)		(1,350)
Total liabilities and equity	(1,580)		(1,350)
Eliminations | WMG Acquisition Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	(4,684)		(4,210)
Total assets	(4,684)		(4,210)
Current liabilities:
Total Warner Music Group Corp. (deficit) equity	(4,684)		(4,210)
Total equity	(4,684)		(4,210)
Total liabilities and equity	$ (4,684)		$ (4,210)