Summary of RSA and RSU Activity (Detail) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Aggregate Intrinsic Value
Stock price used to calculate aggregate intrinsic value		$ 150.09
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value		$ 183	$ 163	$ 142
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		3 years
Restricted Stock Awards
Restricted stock
Beginning balance		466,007
Granted		0	0	0
Vested		(451,297)
Forfeited		(14,710)
Ending balance		0	466,007
Weighted-Average Grant Date Fair Value
Beginning balance		$ 63.37
Granted		0.00
Vested		63.39
Forfeited		72.25
Ending balance		$ 0.00	$ 63.37
Weighted-Average Remaining Contactual Term
Outstanding at September 30, 2018		0 years
Aggregate Intrinsic Value
Outstanding at September 30, 2018	[1]	$ 0
Restricted Stock Units
Restricted stock
Beginning balance		4,673,701
Granted		2,832,984
Vested		(1,937,132)
Forfeited		(365,099)
Ending balance		5,204,454	4,673,701
Weighted-Average Grant Date Fair Value
Beginning balance		$ 80.37
Granted		111.11	$ 81.67	$ 79.77
Vested		79.76
Forfeited		92.31
Ending balance		$ 96.50	$ 80.37
Weighted-Average Remaining Contactual Term
Outstanding at September 30, 2018		10 months 17 days
Aggregate Intrinsic Value
Outstanding at September 30, 2018	[1]	$ 781,000,000

[1] Calculated by multiplying the closing stock price on the last trading day of fiscal 2018 of $150.09 by the number of instruments.