Share Repurchases in the Open Market (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013		Mar. 31, 2013
Stockholders' Equity Note [Abstract]
Shares repurchased in the open market (1)	12	[1]	20	[1]
Weighted-average repurchase price per share	$ 157.24		$ 152.19
Total cost	$ 1,820		$ 3,073

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