Stockholders' Equity Share Repurchases in the Open Market (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions			12 Months Ended
		Sep. 30, 2016	Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2014
Class of Stock [Line Items]
Shares repurchased in the open market		1
Total cost		$ 120	$ 6,987		$ 2,910	$ 4,118
Class A common stock
Class of Stock [Line Items]
Shares repurchased in the open market	[2]		91	[1]	44
Average repurchase price per share	[3]		$ 77.05	[1]	$ 65.98
Total cost			$ 6,987	[1]	$ 2,910

[1] (in millions, except per share data)2016 (1) 2015Shares repurchased in the open market(2)91 44Average repurchase price per share(3)$77.05 $65.98Total cost$6,987 $2,910

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

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