Stockholders' Equity - Number of Shares of Class A Common Shares Outstanding on an As-Converted Basis (Detail) shares in Millions		Dec. 31, 2015 shares	Sep. 30, 2015 shares	Mar. 19, 2015
Schedule of Common Stock as Converted [Line Items]
As-converted Class A Common Stock	[1]	2,409
Class A common stock
Schedule of Common Stock as Converted [Line Items]
Shares Outstanding		1,926	1,950
As-converted Class A Common Stock	[1]	1,926
Class B common stock
Schedule of Common Stock as Converted [Line Items]
Shares Outstanding		245	245
Conversion Rate Into Class A Common Stock	[2]	1.6483		1.6483
As-converted Class A Common Stock	[1]	405
Class C common stock
Schedule of Common Stock as Converted [Line Items]
Shares Outstanding		19	20
Conversion Rate Into Class A Common Stock		4		4
As-converted Class A Common Stock	[1]	78

[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] 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.