Debt (Senior Notes) (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt	$ 5,773,716,000	$ 5,431,948,000
Interest rate swaps | 2018 Senior Notes
Debt Instrument [Line Items]
Long-term debt	500,000,000
Debt instrument, interest rate at period end	3.25%
Senior Notes | 2018 Senior Notes
Debt Instrument [Line Items]
Long-term debt	822,008,000	826,974,000
Discount on debt	9,300,000	9,700,000
Fair value adjustment	31,300,000	36,600,000
Senior Notes | 2020 Senior Notes
Debt Instrument [Line Items]
Long-term debt	1,013,038,000	1,013,372,000
Premium on debt	13,000,000	13,400,000
Senior Notes | 2023 Senior Notes
Debt Instrument [Line Items]
Long-term debt	748,484,000	748,452,000
Discount on debt	$ 1,500,000	$ 1,500,000