Share-Based Compensation - Summary of SARs Outstanding (Detail) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2017 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	7,027
SARs, granted (shares) | shares	996
SARs, exercised (shares) | shares	(1,445)
SARs, forfeited, canceled or expired (shares) | shares	(112)
SARs, ending balance (shares) | shares	6,466
SARs, Vested and expected to vest at ending balance (shares) | shares	6,215
SARs, Exercisable at ending balance (shares) | shares	3,952
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	$ 103.83
SARs, weighted average exercise price, granted (USD per share) | $ / shares	170.69
SARs, weighted average exercise price, exercised (USD per share) | $ / shares	83.81
SARs, weighted average exercise price, forfeited, canceled or expired (USD per share) | $ / shares	142.04
SARs, weighted average exercise price, ending balance (USD per share) | $ / shares	117.94
SARs, weighted average exercise price, vested and expected to vest (USD per share) | $ / shares	116.54
SARs, weighted average exercise price, exercisable (USD per share) | $ / shares	$ 96.00
SARs, weighted average remaining contractual term	6 years 2 months 26 days
SARs, weighted average remaining contractual term, vested and expected to vest	6 years 1 month 27 days
SARs, weighted average remaining contractual term, exercisable	4 years 11 months 22 days
SARs, aggregate intrinsic value | $	$ 504
SARs, aggregate intrinsic value, vested and expected to vest | $	493
SARs, aggregate intrinsic value, exercisable | $	$ 395