Debt Credit Facility (Details) (USD $)						12 Months Ended			12 Months Ended			12 Months Ended
	Dec. 31, 2012	Nov. 16, 2012 Credit Facility [Member]	Jun. 18, 2010 Credit Facility [Member]	Jun. 17, 2010 Previous Revolving Credit Facility [Member]	Jun. 17, 2010 Previous Term Loan Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]	Dec. 31, 2010 Revolving Credit Facility [Member]	Jun. 18, 2010 Revolving Credit Facility [Member]	Dec. 31, 2012 Term Loan Facility [Member]	Jun. 18, 2010 Term Loan Facility [Member]	Jun. 18, 2010 Swingline Sub-facility [Member]	Dec. 31, 2012 Maximum [Member] Revolving Credit Facility [Member]	Dec. 31, 2012 Minimum [Member] Revolving Credit Facility [Member]	Dec. 31, 2012 Base Rate [Member] Maximum [Member] Credit Facility [Member]	Dec. 31, 2012 Base Rate [Member] Minimum [Member] Credit Facility [Member]	Dec. 31, 2012 Eurocurrency Rate [Member] Maximum [Member] Credit Facility [Member]	Dec. 31, 2012 Eurocurrency Rate [Member] Minimum [Member] Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 2,000,000,000	$ 1,800,000,000				$ 1,500,000,000		$ 500,000,000	$ 50,000,000
Debt Instrument, Basis Spread on Variable Rate														3.00%	1.25%	4.00%	2.25%
Deferred Finance Costs, Net		4,700,000
Additional Borrowing capacity under revolving credit facility upon request									250,000,000
Minimum amount of revolving credit facility increase, upon request									25,000,000
Previous term loan facility balance					490,300,000
Unamortized Debt Issuance Expense	78,600,000							21,900,000
Refinancing charges classified as interest expense							9,300,000
Line Of Credit Facility Commitment Fee Percent, Maximum												0.50%	0.375%
Letter of credit fee as a percentage of the undrawn amount of each letter of credit, Higher range												4.00%	2.25%
Fronting fee as a percentage of the face amount of each letter of credit						0.125%
Term loan facility percentage of periodic repayment									1.25%
Prepayment of Principal									25,000,000
Letters of credit outstanding	79,700,000					105,400,000
Line of Credit Facility, Remaining Borrowing Capacity						$ 1,400,000,000
Interest Rate Over And Above Libor Rate						3.00%
Term loan interest rate over and above LIBRO rate									3.21%