Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended	9 Months Ended
		Jun. 30, 2018	Jun. 30, 2018	Jul. 27, 2018	Jan. 30, 2018
Stockholders Equity Note [Line Items]
Stock Repurchased and Retired During Period, Shares	[1],[2]	14	47
Stock Repurchased and Retired During Period, Value	[2]	$ 1,754	$ 5,604
Deposits To Litigation Escrow Account		600	600
Recovery Through Conversion Rate Adjustment		6	56
Stock Repurchase Program, Authorized Amount					$ 7,500
Stock Repurchase Remaining Authorized Amount		5,800	5,800
Dividends, Cash		$ 487	$ 1,400
Class A common stock
Stockholders Equity Note [Line Items]
Reduction In As-Converted Stock, Shares			52
Reduction in As-Converted Stock, Average Price Per Share			$ 120.37
Subsequent Event | Class A common stock
Stockholders Equity Note [Line Items]
Dividends Payable, Amount Per Share				$ 0.21

[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 nine months ended June 30, 2018. These amounts include repurchases traded but not yet settled on or before September 30, 2017 for the nine months, or March 31, 2018 for the three months, and exclude repurchases traded but not yet settled on or before June 30, 2018.