Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017		Mar. 31, 2017	Apr. 20, 2017	Jan. 31, 2017
Stockholders Equity Note [Line Items]
Stock Repurchased and Retired During Period, Shares	18	[1],[2]	41
Stock Repurchased and Retired During Period, Value	$ 1,576,000,000	[2]	$ 3,469,000,000
Stock Repurchase Remaining Authorized Amount	2,300,000,000		2,300,000,000
Dividends, Cash	$ 396,000,000		795,000,000
Recovery through conversion rate adjustment			$ (120,000,000)
Class A common stock
Stockholders Equity Note [Line Items]
Reduction in As-converted Stock, Shares			43
Reduction in As-converted Stock, Average Price Per Share			$ 83.64
Dividends Payable, Amount Per Share					$ 0.165
Subsequent Event
Stockholders Equity Note [Line Items]
Stock Repurchase Program, Authorized Amount				$ 5,000,000,000.0

[1] All shares repurchased in the open market have been retired and constitute authorized but unissued shares.

[2] Shares repurchased in the open market reflect repurchases settled during the three and six months ended March 31, 2017. These amounts include repurchases traded but not yet settled on or before September 30, 2016 for the six months, or December 31, 2016 for the three months, and exclude repurchases traded but not yet settled on or before March 31, 2017.