Share-based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions		12 Months Ended
	Mar. 19, 2015	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense		$ 67	$ 62	$ 54
Total fair value of RSAs and RSUs vested		$ 163	142	132
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		10 years
Vesting period from the date of grant		3 years
Total intrinsic value from options exercised		$ 178	103	134
Tax Benefit from Exercise of Stock Options		62	$ 35	$ 86
Unrecognized compensation cost		$ 19
Total unrecognized compensation cost related to non-vested options expected to be recognized over a weighted average period (in years)		4 months 24 days
Weighted average remaining contractual term		5 years 4 months 24 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period from the date of grant		3 years
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost		$ 7
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 0.00		$ 63.71
Shares granted | shares		0	0
Weighted average remaining contractual term		2 months 21 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost		$ 215
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 81.67	$ 79.77	$ 62.88
Shares granted | shares		3,268,327
Weighted average remaining contractual term		1 year 7 months 6 days
Performance Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period from the date of grant		3 years	3 years	3 years
Unrecognized compensation cost		$ 33
Weighted average grant date fair value per share | $ / shares		$ 86.37	$ 92.71	$ 69.78
Class A common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock split, conversion ratio	4
Equity Incentive Compensation Plan, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of Class A Common Stock authorized for issuance under EIP or ESPP | shares		236,000,000
Share-based compensation expense under EIP		$ 224	$ 211	$ 184
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of Class A Common Stock authorized for issuance under EIP or ESPP | shares		20,000,000
ESPP discount from market price		15.00%