Long-Term Debt (Credit Facility End of Period Disclosures Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Credit Facility, Name [Member] Credit Facility, Type of Debt [Member] item	Dec. 31, 2012 Credit Facility, Revolving Credit Loans [Member] Line of Credit [Member]	Dec. 31, 2011 Credit Facility, Revolving Credit Loans [Member] Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity		$ 750,000,000
Letters of Credit Outstanding, Amount		37,800,000	37,700,000
Minimum Number of Additional Tranches Available in Future	1
Aggregate Principal Amount of Each Tranche Available in Future	$ 1,000,000,000
Debt, Weighted Average Interest Rate	4.20%