Stockholders' Equity - Share Repurchases in the Open Market (Detail) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	[2]
Stockholders' Equity Note [Abstract]
Shares repurchased in the open market | shares	16	[1]
Average repurchase price per share | $ / shares	$ 110.24	[3]
Total cost | $	$ 1,778

[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 months ended December 31, 2017. These amounts include repurchases traded but not yet settled on or before September 30, 2017 and exclude repurchases traded but not yet settled on or before December 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.