Acquisitions, Disposals and Other Transactions - Additional Information (Detail) £ / shares in Units, £ in Millions, AUD in Millions			1 Months Ended						3 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2015 GBP (£)	Sep. 30, 2016 USD ($)	Sep. 30, 2016 GBP (£) £ / shares	May 31, 2016 USD ($)	Feb. 29, 2016 USD ($) Tranche	Feb. 29, 2016 AUD Tranche	Jul. 31, 2015 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jan. 31, 2016	Sep. 30, 2015 GBP (£)
Schedule Of Business Acquisitions And Divestitures [Line Items]
Restricted cash			$ 0						$ 0	$ 315,000,000
Checkout 51 Mobile Apps ULC [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, cost of acquired entity								$ 13,000,000
Deferred cash consideration related to contingent payments										10,000,000
DIAKRIT International Limited [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, cost of acquired entity						$ 40,000,000
Business acquisition, acquired interest percentage						92.00%
Non-controlling ownership percentage						8.00%
Number of tranches | Tranche						2	2
Option to sell minority interest, period						6 years	6 years
iProperty Group Limited [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, cost of acquired entity						$ 416,000,000
Business acquisition purchase price allocation, amortizable intangible assets						72,000,000
Business acquisition, cost of acquired entity, cash paid						340,000,000
iProperty Group Limited [Member] | REA Group [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Future consideration related to contingent payments						$ 76,000,000
Non-controlling ownership percentage						13.10%
Business acquisition, ownership percentage						86.90%					22.70%
Company ownership percentage						61.60%	61.60%
Business acquisition, cost of acquired entity, cash paid						$ 340,000,000	AUD 482
Minority interest ownership redeemable year									2018
iProperty Group Limited [Member] | REA Group [Member] | Other, Net [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition recognized gain resulting from remeasurement of previously held equity interest										29,000,000
Flatmates [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, cost of acquired entity					$ 19,000,000
Future cash consideration related to contingent payments					$ 15,000,000
Wireless Group plc [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, cost of acquired entity			285,000,000	£ 220
Business acquisition, cost of acquired entity per share | £ / shares				£ 0.315
Assumed debt			23,000,000						$ 23,000,000
Restricted cash			0						0
Business acquisition purchase price allocation, goodwill amount									149,000,000
Business acquisition, cost of acquired entity, cash paid									285,000,000
Wireless Group plc [Member] | Broadcast Licenses [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition purchase price allocation, non-amortizable intangible assets			$ 193,000,000						$ 193,000,000
Unruly Holdings Limited [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, cost of acquired entity	$ 90,000,000	£ 60
Business acquisition purchase price allocation, goodwill amount	68,000,000
Future cash consideration related to contingent payments	86,000,000											£ 56
Future consideration related to contingent payments	40,000,000
Unruly Holdings Limited [Member] | Acquired Technology [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition purchase price allocation, amortizable intangible assets	$ 43,000,000
Finite lived intangible assets, weighted average useful life	7 years	7 years
Unruly Holdings Limited [Member] | Customer Relationships and Trade Names [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition purchase price allocation, amortizable intangible assets	$ 21,000,000
Finite lived intangible assets, weighted average useful life	6 years	6 years
Australian Regional Media [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, cost of acquired entity										$ 30,000,000