Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Debt Instrument [Line Items]
Total interest expense, net	$ 54	$ 49	$ 109	$ 102
Weighted-average interest rate of total debt	6.90%	8.30%	6.90%	8.30%
2014 Debt Refinancing
Debt Instrument [Line Items]
Face or Principal amount of Debt Instrument	1,250		1,250
Senior Notes
Debt Instrument [Line Items]
Scheduled maturities of long-term debt in 2018	765		765
Scheduled to mature	817		817
11.5% Senior Notes due 2018 | 2014 Debt Refinancing
Debt Instrument [Line Items]
Face or Principal amount of Debt Instrument	$ 765		$ 765
Revolving Credit Facility
Debt Instrument [Line Items]
Credit Facility maturity date			Nov. 01, 2017
Extended maturity date of credit facility			Apr. 01, 2019