Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2011	Sep. 30, 2011
4.125% unsecured senior notes
Debt Instrument [Line Items]
Principal amount of unsecured notes issued	$ 550
Debt instrument interest rate stated percentage (as a percent)		4.125%
5.75% unsecured senior notes
Debt Instrument [Line Items]
Principal amount of unsecured notes issued	$ 950
Debt instrument interest rate stated percentage (as a percent)		5.75%