Acquisitions, Disposals and Other Transactions - Additional Information (Detail) AUD in Millions, $ in Millions			1 Months Ended	3 Months Ended
	Jul. 31, 2017 USD ($)	Jul. 31, 2017 AUD	Jul. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)
Schedule Of Business Acquisitions And Divestitures [Line Items]
Goodwill					$ 3,917	$ 3,838
Smartline Home Loans Pty Limited [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition, acquired interest percentage	80.30%		80.30%
Business acquisition, cost of acquired entity, cash paid	$ 55	AUD 70
Non-controlling ownership percentage	19.70%		19.70%
Option to sell minority interest, period				3 years
Minority interest ownership mandatorily redeemable period after closing				4 years
Amount expected to be paid for remaining interest				$ 12
Goodwill	$ 47		$ 47
Smartline Home Loans Pty Limited [Member] | Customer Relationships [Member]
Schedule Of Business Acquisitions And Divestitures [Line Items]
Business acquisition purchase price allocation, intangible assets	$ 19		$ 19
Finite lived intangible assets, weighted average useful life			16 years