Financial Instruments and Risk Concentration (Details)	Dec. 31, 2013	Sep. 30, 2013
2.35% senior notes due September 2016
Financial Instruments and Risk Concentration
Interest rate on senior notes due (as a percent)	2.35%	2.35%
5.10% senior notes due September 2023
Financial Instruments and Risk Concentration
Interest rate on senior notes due (as a percent)	5.10%	5.10%
6.15% senior notes due February 2018
Financial Instruments and Risk Concentration
Interest rate on senior notes due (as a percent)	6.15%
9.25% senior notes due January 2019
Financial Instruments and Risk Concentration
Interest rate on senior notes due (as a percent)	9.25%
5.00% senior notes due September 2020
Financial Instruments and Risk Concentration
Interest rate on senior notes due (as a percent)	5.00%
4.625% senior notes due September 2021
Financial Instruments and Risk Concentration
Interest rate on senior notes due (as a percent)	4.625%