Long-Term Debt (Details) (USD $)	3 Months Ended		1 Months Ended	0 Months Ended	1 Months Ended	2 Months Ended	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 20, 2014	Jan. 31, 2015	Mar. 31, 2015	Dec. 31, 2014	Mar. 19, 2014	Nov. 30, 2014
Long-Term Debt
Long-term debt, net of discounts	$ 4,184,463,000		$ 4,184,463,000			$ 4,184,463,000	$ 3,621,404,000
Accrued interest payable	62,200,000		62,200,000			62,200,000
Deferred financing costs	7,000,000	1,890,000
2024 Senior Notes, 4.875% interest, issued March 2015 and due December 2024
Long-Term Debt
Debt instrument, stated interest rate percentage	4.875%		4.875%			4.875%
Accrued interest on notes issued			9,000,000
Revolving credit facility
Long-Term Debt
Long-term debt, net of discounts							97,600,000
Applicable interest rate (as a percent)							4.50%
Credit facility current lending capacity				1,300,000,000
Extension of maturity				18 months
Accordion option to increase borrowing capacity under the Credit Facility				500,000,000				250,000,000
Deferred financing costs		1,900,000
Letters of credit maximum borrowing capacity	150,000,000		150,000,000			150,000,000
Short-term swingline loan maximum borrowing capacity	10,000,000		10,000,000			10,000,000
Minimum Interest Coverage Ratio	2.5
Maximum leverage ratio prior to Collateral Release Date					5.25	5.5	5.5
Maximum leverage ratio after Collateral Release Date	5.00
Borrowings outstanding	0		0			0
Letters of credit outstanding amount	11,300,000		11,300,000			11,300,000
Unused borrowing capacity	1,288,700,000		1,288,700,000			1,288,700,000
Amount available for borrowing based on financial covenant requirements	1,040,200,000		1,040,200,000			1,040,200,000
Revolving credit facility | Alternate Base Rate Loans | Minimum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)	0.50%
Margin after Collateral Release Date (as a percent)	0.125%
Revolving credit facility | Alternate Base Rate Loans | Maximum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)	1.50%
Margin after Collateral Release Date (as a percent)	1.00%
Revolving credit facility | Alternate Base Rate Loans | Prime rate
Long-Term Debt
Basis of variable interest rate	prime rate
Revolving credit facility | Alternate Base Rate Loans | Federal funds effective swap rate
Long-Term Debt
Basis of variable interest rate	Federal Funds Rate
Spread on variable rate basis (as a percent)	0.50%
Revolving credit facility | Alternate Base Rate Loans | One month LIBOR
Long-Term Debt
Basis of variable interest rate	One month LIBOR
Spread on variable rate basis (as a percent)	1.00%
Revolving credit facility | LIBO Rate Loans | Minimum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)	1.50%
Margin after Collateral Release Date (as a percent)	1.125%
Revolving credit facility | LIBO Rate Loans | Maximum
Long-Term Debt
Margin prior to Collateral Release Date (as a percent)	2.50%
Margin after Collateral Release Date (as a percent)	2.00%
Revolving credit facility | LIBO Rate Loans | One month LIBOR
Long-Term Debt
Basis of variable interest rate	LIBOR
Senior Notes
Long-Term Debt
Estimated aggregate fair value of debt	4,297,000,000		4,297,000,000			4,297,000,000	3,563,000,000
Senior Notes | 2020 Senior Notes, 6.75% interest, issued November 2010 and due November 2020
Long-Term Debt
Long-term debt, net of discounts	500,000,000		500,000,000			500,000,000	500,000,000
Debt instrument, stated interest rate percentage	6.75%		6.75%			6.75%	6.75%
Senior Notes | 2021 Senior Notes, 6.5% interest, issued February and March 2011 and due August 2021
Long-Term Debt
Long-term debt, net of discounts	324,603,000		324,603,000			324,603,000	324,587,000
Debt instrument, stated interest rate percentage	6.50%		6.50%			6.50%	6.50%
Long-term debt, discounts	397,000		397,000			397,000	413,000
Senior Notes | 2022 Senior Notes, 6.25% interest, issued October 2011 and due June 2022
Long-Term Debt
Long-term debt, net of discounts	455,000,000		455,000,000			455,000,000	455,000,000
Debt instrument, stated interest rate percentage	6.25%		6.25%			6.25%	6.25%
Senior Notes | 2023A Senior Notes, 5.5% interest, issued August 2012 and due February 2023
Long-Term Debt
Long-term debt, net of discounts	744,385,000		744,385,000			744,385,000	744,217,000
Debt instrument, stated interest rate percentage	5.50%		5.50%			5.50%	5.50%
Long-term debt, discounts	5,615,000		5,615,000			5,615,000	5,783,000
Senior Notes | 2023B Senior Notes, 4.5% interest, issued January 2013 and due July 2023
Long-Term Debt
Long-term debt, net of discounts	1,000,000,000		1,000,000,000			1,000,000,000	1,000,000,000
Debt instrument, stated interest rate percentage	4.50%		4.50%			4.50%	4.50%
Senior Notes | 2024 Senior Notes, 4.875% interest, issued November 2014 and March 2015, due December 2024
Long-Term Debt
Long-term debt, net of discounts	1,160,475,000		1,160,475,000			1,160,475,000	500,000,000
Debt instrument, stated interest rate percentage	4.875%		4.875%			4.875%
Long-term debt, premium	10,475,000		10,475,000			10,475,000
Senior Notes | 2024 Senior Notes, 4.875% interest, issued March 2015 and due December 2024
Long-Term Debt
Aggregate principal amount	650,000,000		650,000,000			650,000,000
Proceeds from issuance of senior notes, net of underwriting fees and the other expenses of the offering			653,600,000
Senior Notes | 2024 Senior Notes, 4.875% interest, issued November 2014 and due December 2024
Long-Term Debt
Debt instrument, stated interest rate percentage									4.875%
Aggregate principal amount									$ 500,000,000