Share-Based Compensation - Summary of Stock Options 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, Options, Outstanding [Roll Forward]
Stock options, beginning balance (shares) | shares	495
Stock options, exercised (shares) | shares	(186)
Stock options, forfeited, canceled or expired (shares) | shares	(6)
Stock options, ending balance (shares) | shares	303
Stock options, vested at ending balance (shares) | shares	303
Stock options, exercisable at ending balance (shares) | shares	303
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average exercise price, beginning of period (USD per share) | $ / shares	$ 79.99
Weighted average exercise price, exercised (USD per share) | $ / shares	77.66
Weighted average exercise price, forfeited, canceled or expired (USD per share) | $ / shares	81.30
Weighted average exercise price, end of period (USD per share) | $ / shares	81.40
Stock options, weighted average exercise price, vested at ending balance (USD per share) | $ / shares	81.40
Stock options, weighted average exercise price, exercisable at ending balance (USD per share) | $ / shares	$ 81.40
Stock options, weighted average remaining contractual term, balance at ending balance	2 years 6 months 21 days
Stock options, weighted average remaining contractual term, vested at ending balance	2 years 6 months 21 days
Stock options, weighted average remaining contractual term, exercisable at ending balance	2 years 6 months 21 days
Stock options, aggregate intrinsic value, balance at ending balance | $	$ 35
Stock options, aggregate intrinsic value, vested at ending balance | $	35
Stock options, aggregate intrinsic value, exercisable at ending balance | $	$ 35