Stock-Based Compensation - Additional Information (Detail) - USD ($)		9 Months Ended	12 Months Ended
		Sep. 30, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Mar. 08, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, authorized shares						8,900,000
Percentage of vesting in first anniversary			30.00%
Percentage of vesting in second anniversary			30.00%
Percentage of vesting in third anniversary			40.00%
Stock based compensation outstanding units			35,769
Cash settled awards			$ 1,000,000	$ 1,000,000
Net stock-based compensation expense			$ 8,000,000	$ 9,000,000	$ 8,000,000
Closing common stock price			$ 31.56
Stock Options, Weighted Average Grant Date Fair Value, Granted			$ 15.68
Supplemental 401(k) Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Supplemental retirement savings plan, aggregate value of the accounts, shares			150,000	146,000
Supplemental retirement savings plan aggregate value of the accounts paid in cash			$ 1,000,000	$ 1,000,000
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price equal to market price on the date of grant			100.00%
Vesting period (in years)			3 years
Expiration period, years			10 years
Unrecognized compensation cost			$ 2,000,000
Weighted-average period, years			9 months 18 days
Intrinsic value of options exercised			$ 2,000,000	12,000,000	5,000,000
Cash received from exercises			$ 4,000,000	$ 9,000,000	$ 5,000,000
Stock Options, Weighted Average Grant Date Fair Value, Granted		$ 12.51	$ 15.68	$ 18.36
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)			3 years
Stock based compensation outstanding units	[1]		735,000	946,000
Unrecognized compensation cost			$ 12,000,000
Weighted-average period, years			1 year 3 months 18 days
Estimated weighted average grant date fair value			$ 45.85	$ 47.63	$ 35.28
Intrinsic value of restricted stock units vested			$ 14,000,000	$ 17,000,000	$ 16,000,000
Awards granted	[1]		345,000
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)			3 years
Awards granted			0	0	0
Restricted Stock | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic value of restricted stock units vested			$ 1,000,000	$ 1,000,000	$ 1,000,000

[1] The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.