Share-Based Compensation - Summary of SARs Outstanding (Detail) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
SARs, beginning balance (shares) | shares	6,899
SARs, granted (shares) | shares	874
SARs, exercised (shares) | shares	(1,295)
SARs, forfeited, canceled or expired (shares) | shares	(140)
SARs, ending balance (shares) | shares	6,337
SARs, Vested and expected to vest at ending balance (shares) | shares	6,152
SARs, Exercisable at ending balance (shares) | shares	4,483
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
SARs, weighted average exercise price, beginning balance (USD per share) | $ / shares	$ 144.84
SARs, weighted average exercise price, granted (USD per share) | $ / shares	255.22
SARs, weighted average exercise price, exercised (USD per share) | $ / shares	101.81
SARs, weighted average exercise price, forfeited, canceled or expired (USD per share) | $ / shares	220.82
SARs, weighted average exercise price, ending balance (USD per share) | $ / shares	167.17
SARs, weighted average exercise price, vested and expected to vest (USD per share) | $ / shares	165.02
SARs, weighted average exercise price, exercisable (USD per share) | $ / shares	$ 137.60
SARs, weighted average remaining contractual term	5 years 7 months 28 days
SARs, weighted average remaining contractual term, vested and expected to vest	5 years 6 months 29 days
SARs, weighted average remaining contractual term, exercisable	4 years 7 months 2 days
SARs, aggregate intrinsic value | $	$ 441
SARs, aggregate intrinsic value, vested and expected to vest | $	440
SARs, aggregate intrinsic value, exercisable | $	$ 429