Share-Based Compensation - Summary of SARs Outstanding (Detail) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2019 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	7,986
SARs, granted (shares) | shares	859
SARs, exercised (shares) | shares	(1,779)
SARs, forfeited, canceled or expired (shares) | shares	(168)
SARs, ending balance (shares) | shares	6,899
SARs, Vested and expected to vest at ending balance (shares) | shares	6,692
SARs, Exercisable at ending balance (shares) | shares	4,833
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	$ 125.73
SARs, weighted average exercise price, granted (USD per share) | $ / shares	242.10
SARs, weighted average exercise price, exercised (USD per share) | $ / shares	102.14
SARs, weighted average exercise price, forfeited, canceled or expired (USD per share) | $ / shares	186.18
SARs, weighted average exercise price, ending balance (USD per share) | $ / shares	144.84
SARs, weighted average exercise price, vested and expected to vest (USD per share) | $ / shares	142.87
SARs, weighted average exercise price, exercisable (USD per share) | $ / shares	$ 117.65
SARs, weighted average remaining contractual term	5 years 8 months 12 days
SARs, weighted average remaining contractual term, vested and expected to vest	5 years 7 months 13 days
SARs, weighted average remaining contractual term, exercisable	4 years 8 months 8 days
SARs, aggregate intrinsic value | $	$ 746
SARs, aggregate intrinsic value, vested and expected to vest | $	737
SARs, aggregate intrinsic value, exercisable | $	$ 654