Stockholders' Equity - Share Repurchases in the Open Market (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	[2]	Mar. 31, 2017
Stockholders' Equity Note [Abstract]
Shares repurchased in the open market	18	[1]	41
Average repurchase price per share	$ 88.45	[3]	$ 83.59
Total cost	$ 1,576		$ 3,469

[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.

[3] Figures in the table may not recalculate exactly due to rounding. Average repurchase price per share is calculated based on unrounded numbers.