Long-Term Debt (Details Textuals) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Nov. 30, 2010
Debt Instrument [Line Items]
Unsecured senior notes issued	$ 700	$ 700	$ 700
Long Term Debt (Textuals) [Abstract]
Fair value of 2013 and 2015 Notes based on estimated market prices	707	687
Notes redemption price	101% of the aggregate principal amount of such Notes plus accrued and unpaid interest
Percentage of aggregate principal amount of Notes	101.00%
Unsecured revolving facility loans aggregate available amount to be drawn	500
Credit Facility, interest rate description	Eurodollar Rate Committed Loan will accrue interest at the British Bankers Association LIBOR, or BBA LIBOR, plus the Applicable Rate. US Dollar Rate Committed Loan will accrue interest at rates that are equal to the higher of (a) the Federal Funds Rate plus 0.5% (b) Bank of America’s “prime rate” as announced from time to time, or (c) BBA LIBOR plus the Applicable Rate.
Interest Rate of Committed Loan	0.50%
Description of debt instrument on variable rate basis	LIBOR
Amount available to increase commitment under credit facility	100
Credit Facility financial covenants that require us to maintain certain financial ratios	Financial covenants require us to maintain a consolidated leverage ratio of no more than 3.25 to 1.00 and a consolidated interest coverage ratio of no less than 3.00 to 1.00
Leverage Ratio	3.25%
Interest Coverage Ratio	3.00%
1.500% Fixed Rate Notes Due 2013 [Member]
Debt Instrument [Line Items]
Unsecured senior notes issued			300
Fixed interest rate on senior note			1.50%
Original discount rate on notes issued			99.694%
2.375% Fixed Rate Notes Due 2015 [Member]
Debt Instrument [Line Items]
Unsecured senior notes issued			$ 400
Fixed interest rate on senior note			2.375%
Original discount rate on notes issued			99.444%