Capital Structure - Additional Information (Detail) - Common Stock [Member] - USD ($)	9 Months Ended
	Sep. 30, 2017	Oct. 31, 2017	Nov. 30, 2016
Capital Structure [Line Items]
Repurchase of common stock, shares	(17,847,000)
Repurchase price of common stock, per share	$ 82.62
Share repurchase program, remaining authorized repurchase amount	$ 379,000,000
Share repurchase program authorized amount			$ 2,000,000,000
Subsequent Event [Member]
Capital Structure [Line Items]
Share repurchase program authorized amount		$ 2,000,000,000