Guarantor and Non-Guarantor Subsidiaries Financial Information - Consolidating Balance Sheet Unaudited (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Mar. 31, 2016
Current assets:
Cash and equivalents	$ 776	$ 647	$ 455	$ 359	$ 359
Accounts receivable, net	499	404
Inventories	38	39
Royalty advances expected to be recouped within one year	142	141
Prepaid and other current assets	47	44
Total current assets	1,502	1,275
Royalty advances expected to be recouped after one year	175	172
Property, plant and equipment, net	213	213
Goodwill	1,688	1,685
Intangible assets subject to amortization, net	2,045	2,090
Intangible assets not subject to amortization	117	117
Deferred tax assets, net	61	97
Other assets	74	69
Total assets	5,875	5,718
Current liabilities:
Accounts payable	166	208
Accrued royalties	1,406	1,263
Accrued liabilities	401	365
Accrued interest	25	41
Deferred revenue	201	197
Other current liabilities	35	26
Total current liabilities	2,234	2,100
Long-term debt	2,818	2,811
Deferred tax liabilities, net	196	190
Other noncurrent liabilities	306	309
Total liabilities	5,554	5,410
Total Warner Music Group Corp. equity	307	293
Noncontrolling interest	14	15
Total equity	321	308
Total liabilities and equity	5,875	5,718
Reportable Legal Entities | Guarantor Subsidiaries
Current assets:
Cash and equivalents	435	347	182		180
Accounts receivable, net	247	214
Inventories	13	12
Royalty advances expected to be recouped within one year	86	89
Prepaid and other current assets	14	15
Total current assets	795	677
Due from (to) parent companies	(4)	96
Investments in and advances to consolidated subsidiaries	1,453	1,312
Royalty advances expected to be recouped after one year	106	109
Property, plant and equipment, net	139	139
Goodwill	1,368	1,368
Intangible assets subject to amortization, net	1,006	1,029
Intangible assets not subject to amortization	71	71
Deferred tax assets, net	53	89
Other assets	47	45
Total assets	5,034	4,935
Current liabilities:
Accounts payable	87	135
Accrued royalties	791	732
Accrued liabilities	175	144
Deferred revenue	148	125
Other current liabilities	4	3
Total current liabilities	1,205	1,139
Other noncurrent liabilities	195	196
Total liabilities	1,400	1,335
Total Warner Music Group Corp. equity	3,630	3,596
Noncontrolling interest	4	4
Total equity	3,634	3,600
Total liabilities and equity	5,034	4,935
Reportable Legal Entities | Non-Guarantor Subsidiaries
Current assets:
Cash and equivalents	341	300	273		179
Accounts receivable, net	252	190
Inventories	25	27
Royalty advances expected to be recouped within one year	56	52
Prepaid and other current assets	33	29
Total current assets	707	598
Due from (to) parent companies	(496)	(514)
Royalty advances expected to be recouped after one year	69	63
Property, plant and equipment, net	74	74
Goodwill	320	317
Intangible assets subject to amortization, net	1,039	1,061
Intangible assets not subject to amortization	46	46
Deferred tax assets, net	8	8
Other assets	20	17
Total assets	1,787	1,670
Current liabilities:
Accounts payable	79	73
Accrued royalties	615	531
Accrued liabilities	226	221
Deferred revenue	53	72
Other current liabilities	31	23
Total current liabilities	1,004	920
Deferred tax liabilities, net	196	190
Other noncurrent liabilities	110	112
Total liabilities	1,310	1,222
Total Warner Music Group Corp. equity	467	437
Noncontrolling interest	10	11
Total equity	477	448
Total liabilities and equity	1,787	1,670
Reportable Legal Entities | Warner Music Group Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	391	377
Total assets	391	377
Current liabilities:
Total Warner Music Group Corp. equity	391	377
Total equity	391	377
Total liabilities and equity	391	377
Reportable Legal Entities | WMG Acquisition Corp.
Current assets:
Due from (to) parent companies	500	418
Investments in and advances to consolidated subsidiaries	2,644	2,721
Other assets	7	7
Total assets	3,151	3,146
Current liabilities:
Accrued interest	25	41
Total current liabilities	25	41
Long-term debt	2,818	2,811
Other noncurrent liabilities	1	1
Total liabilities	2,844	2,853
Total Warner Music Group Corp. equity	307	293
Total equity	307	293
Total liabilities and equity	3,151	3,146
Reportable Legal Entities | WMG Acquisition Corp. Consolidated
Current assets:
Cash and equivalents	776	647	$ 455		$ 359
Accounts receivable, net	499	404
Inventories	38	39
Royalty advances expected to be recouped within one year	142	141
Prepaid and other current assets	47	44
Total current assets	1,502	1,275
Royalty advances expected to be recouped after one year	175	172
Property, plant and equipment, net	213	213
Goodwill	1,688	1,685
Intangible assets subject to amortization, net	2,045	2,090
Intangible assets not subject to amortization	117	117
Deferred tax assets, net	61	97
Other assets	74	69
Total assets	5,875	5,718
Current liabilities:
Accounts payable	166	208
Accrued royalties	1,406	1,263
Accrued liabilities	401	365
Accrued interest	25	41
Deferred revenue	201	197
Other current liabilities	35	26
Total current liabilities	2,234	2,100
Long-term debt	2,818	2,811
Deferred tax liabilities, net	196	190
Other noncurrent liabilities	306	309
Total liabilities	5,554	5,410
Total Warner Music Group Corp. equity	307	293
Noncontrolling interest	14	15
Total equity	321	308
Total liabilities and equity	5,875	5,718
Reportable Legal Entities | WMG Holdings Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	391	377
Total assets	391	377
Current liabilities:
Total Warner Music Group Corp. equity	391	377
Total equity	391	377
Total liabilities and equity	391	377
Eliminations
Current assets:
Investments in and advances to consolidated subsidiaries	(782)	(754)
Total assets	(782)	(754)
Current liabilities:
Total Warner Music Group Corp. equity	(782)	(754)
Total equity	(782)	(754)
Total liabilities and equity	(782)	(754)
Eliminations | WMG Acquisition Corp.
Current assets:
Investments in and advances to consolidated subsidiaries	(4,097)	(4,033)
Total assets	(4,097)	(4,033)
Current liabilities:
Total Warner Music Group Corp. equity	(4,097)	(4,033)
Total equity	(4,097)	(4,033)
Total liabilities and equity	$ (4,097)	$ (4,033)