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, 2016	Mar. 31, 2016
Stockholders' Equity Note [Abstract]
Shares repurchased in the open market	[1]	24	50
Average repurchase price per share	[2]	$ 72.23	$ 75.47
Total cost		$ 1,750	$ 3,765

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

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