Share-Based Compensation Plans - Summary of Company's Share Awards (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant date intrinsic value of share awards	$ 107.13	$ 107.13	$ 107.13
Deferred Equity Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested units	18	19
Units, Granted	9	3
Units, Vested	(7)	(2)
Units, Forfeited	(1)	(2)
Unvested units	19	18	19
Unvested units, Fair Value	$ 135.00	$ 132.92
Fair Value, Granted	135.00	132.92
Fair Value, Vested	135.00	132.92
Fair Value, Forfeited	135.00	132.92
Unvested units, Fair Value	142.21	135.00	$ 132.92
Unvested units, Weighted-Average Grant-Date Intrinsic Value	107.13	107.13
Weighted-Average Grant-Date Intrinsic Value, Granted	107.13	107.13
Weighted-Average Grant-Date Intrinsic Value, Vested	107.13	107.13
Weighted-Average Grant-Date Intrinsic Value, Forfeited	107.13	107.13
Unvested units, Weighted-Average Grant-Date Intrinsic Value	$ 107.13	$ 107.13	$ 107.13
Matching Equity Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested units	25	24
Units, Granted	9	3
Units, Vested	(5)
Units, Forfeited	(1)	(2)
Unvested units	28	25	24
Unvested units, Intrinsic Value	$ 27.87	$ 25.79
Vested	27.87	25.79
Forfeited	27.87	25.79
Unvested units, Intrinsic Value	35.08	27.87	$ 25.79
Unvested units, Weighted-Average Grant-Date Intrinsic Value	0	0
Unvested units, Weighted-Average Grant-Date Intrinsic Value	$ 0	$ 0	$ 0