Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended		6 Months Ended
	Feb. 01, 2019	Aug. 31, 2018	Aug. 31, 2017	Dec. 31, 2018	May 31, 2013
Class of Stock [Line Items]
Cash dividends per common share, date of dividend payable		Oct. 17, 2018	Oct. 18, 2017
Cash dividends per common share, date of record for dividend		Sep. 12, 2018	Sep. 13, 2017
Subsequent Event [Member]
Class of Stock [Line Items]
Cash dividends per common share, date of dividend payable	Apr. 17, 2019
Cash dividends per common share, date of record for dividend	Mar. 13, 2019
Class A Common Stock [Member]
Class of Stock [Line Items]
Aggregate amount of shares authorized to be repurchased					$ 500
Number of shares repurchased				0.0
Cash dividends declared per share of common stock		$ 0.10	$ 0.10
Class A Common Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Number of shares repurchased	5.2
Remaining authorized amount under stock repurchase program	$ 429
Aggregate cost of shares repurchased	$ 71
Class B Common Stock [Member]
Class of Stock [Line Items]
Cash dividends declared per share of common stock		$ 0.10	$ 0.10