Benefit Plans - Restricted Stock Units Activity and Related Information (Details) - Restricted stock units $ / shares in Units, shares in Thousands, $ in Millions	9 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Number of Restricted Stock Units
Beginning balance (in shares) | shares	97,571
RSUs granted (in shares) | shares	43,340
RSUs vested (in shares) | shares	(41,292)
RSUs canceled (in shares) | shares	(4,884)
Ending balance (in shares) | shares	94,735
Weighted-Average Grant Date Fair Value Per RSU
Beginning balance (in dollars per share) | $ / shares	$ 110.33
RSUs granted (in dollars per share) | $ / shares	160.79
RSUs vested (in dollars per share) | $ / shares	111.62
RSUs canceled (in dollars per share) | $ / shares	126.32
Ending balance (in dollars per share) | $ / shares	$ 132.03
Aggregate Fair Value
Aggregate fair value of restricted stock units | $	$ 17,536