Benefit Plans - Restricted Stock Units Activity and Related Information (Detail) - Restricted Stock Units $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Number of Restricted Stock Units
Beginning balance (in shares) | shares	99,089
Restricted stock units granted (in shares) | shares	42,882
Restricted stock units vested (in shares) | shares	(18,535)
Restricted stock units cancelled (in shares) | shares	(1,577)
Ending balance (in shares) | shares	121,859
Weighted-Average Grant Date Fair Value Per Share
Beginning balance (in dollars per share) | $ / shares	$ 97.54
Restricted stock units granted (in dollars per share) | $ / shares	117.95
Restricted stock units vested (in dollars per share) | $ / shares	92.65
Restricted stock units cancelled (in dollars per share) | $ / shares	105.01
Ending balance (in dollars per share) | $ / shares	$ 105.37
Aggregate Intrinsic Value
Aggregate intrinsic value of restricted stock units | $	$ 14,114