Stockholders' Equity Effect of Escrow Funding on the Company Repurchaseing its Common Stock (Details) shares in Millions, $ in Millions			12 Months Ended
		Sep. 30, 2016 conversion_rate shares	Sep. 30, 2016 USD ($) conversion_rate	Mar. 19, 2015 conversion_rate
Class of Stock [Line Items]
As-converted class B common stock outstanding after deposits	[1]	2,422
Deposit into Litigation Escrow
Class of Stock [Line Items]
Deposits under the retrospective responsibility plan | $			$ 0
Class A common stock
Class of Stock [Line Items]
As-converted class B common stock outstanding after deposits	[1],[2]	1,871
Class B common stock
Class of Stock [Line Items]
Common stock, conversion rate | conversion_rate	[3]	1.6483	1.6483	1.6483
As-converted class B common stock outstanding after deposits	[1]	405

[1] Figures in the table may not recalculate exactly due to rounding. As-converted class A common stock is calculated based on unrounded numbers.

[2] {F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOmVhOWM1MDkzNjQ1MjRmNzk4OTM0M2I5ZDEyODM0M2JlfFRleHRTZWxlY3Rpb246OENBNzc3NzIxMjY1M0Y0NTY4MDI2RUY3NTNDRjY1NjMM}

[3] The class B to class A common stock conversion rate is presented on a rounded basis. Conversion calculations for dividend payments are based on a conversion rate rounded to the tenth decimal.