Long-Term Debt and Credit Facilities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Line of Credit Facility, Initiation Date	Aug. 22, 2012
Line of Credit Facility, Additional Borrowing Capacity	$ 500
Line of Credit Facility, Commitment Fee Description	5 to 22.5
Line of Credit Facility, Interest Rate Description	bears interest at LIBOR, as defined in the 2012 Facility agreement, plus an applicable margin ranging from 57.5 to 127.5 basis points
Additional borrowing capacity available under all of its existing credit facilities	1,056
Long-term debt, weighted-average interest rate	3.00%
Issuance of long-term debt, unamortized debt issuance costs	11
Debt Instrument, Fair Value Disclosure	1,876	1,837
Senior Unsecured Revolving Credit Facility Due 2017 [Member]
Credit facility	1,000
Expiration date	Aug. 22, 2017
Senior Unsecured Revolving Credit Facility Due 2013 [Member]
Credit facility	1,000
Expiration date	Aug. 05, 2013
Maximum Borrowing Capacity, Multicurrency Sublimit [Member]
Credit facility	500
Maximum Borrowing Capacity, Letter of Credit Sublimit [Member]
Credit facility	$ 100