Credit Facilities and Long-Term Debt (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Letter of Credit	Sep. 30, 2012 Revolving Credit Facility	Sep. 30, 2012 Senior Notes	Sep. 30, 2012 Senior Notes Due 2016, 3.550%		Dec. 31, 2011 Senior Notes Due 2016, 3.550%		Sep. 30, 2012 Senior Notes Due 2016, 3.550% Senior Notes	Sep. 30, 2012 Senior Notes Due 2021, 4.875%		Dec. 31, 2011 Senior Notes Due 2021, 4.875%		Sep. 30, 2012 Senior Notes Due 2021, 4.875% Senior Notes
Credit Facilities and Long-Term Debt [Abstract]
Interest on notes due						3.55%					4.875%
Fair value of senior notes due						$ 643		$ 625			$ 680		$ 642
Debt instrument aggregate principal amount						600	[1]	600	[1]	0	600	[1]	600	[1]	600
Gross proceeds from notes issue	0	1,189			1,200
Debt Issuance Cost					9
Interest payment failure period					30 days
Other covenant default period after servicing of notice					90 days
Percentage of holding required for servicing of notice					25.00%
Redemption price percentage					101.00%
Debt instrument aggregate principal amount			$ 100	$ 600
Interest rate per annum, effective rate				1.00%
Maximum leverage ratio				3.50

[1] The fair value of our Senior Notes (as defined below) as of September 30, 2012 was determined using quoted prices in active markets for identical securities, which are considered Level 1 inputs. As of December 31, 2011, the fair value of our Senior Notes was determined using prices for the identical security obtained from an external pricing service, which are considered Level 2 inputs. As of September 30, 2012 and December 31, 2011, the fair value of our Senior Notes due 2016 was $643 million and $625 million, respectively, and the fair value of our Senior Notes due 2021 was $680 million and $642 million, respectively.