Long-Term Debt (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013 DebtInstrument		Dec. 31, 2011	Dec. 31, 2012
Long Term Debt [Roll Forward]
Long-term debt, beginning balance	$ 8,942,568,000
Payments and Retirements	(517,129,000)
New Borrowings	0
Long-term debt, ending balance	8,425,439,000
Less: Debt (Discount)/Premium	1,189,000			(71,000)
Less: Current Portion	(57,899,000)			(560,550,000)
Principal Outstanding	8,368,729,000			8,381,947,000
Interest Rate (in hundredths)	7.94%	[1]
Senior Notes [Abstract]
Principal Outstanding	8,425,439,000
Weighted average interest rate (in hundredths)	7.94%	[1]
Principal payments by year [Abstract]
Principal Payments 2013 (remaining nine months)	43,420,000
Principal Payments 2014	257,916,000
Principal Payments 2015	732,746,000
Principal Payments 2016	345,466,000
Principal Payments 2017	1,041,186,000
Principal Payments 2018	600,534,000
Unsecured Letter of Credit Facility [Member]
Credit facilities [Abstract]
Line of credit facility maximum borrowing capacity	20,000,000		190,000,000	40,000,000
Line of credit initiation date	Sep. 08, 2010
Line of credit facility expiration date			Sep. 30, 2011
Exercised extension of commitment				100,000,000
Number of letters of credit	2
Unsecured Letter of Credit Facility [Member] | March 2013 [Member]
Credit facilities [Abstract]
Line of credit facility maximum borrowing capacity				20,000,000
Line of credit facility expiration date	Mar. 31, 2013
Unsecured Letter of Credit Facility [Member] | September 2013 [Member]
Credit facilities [Abstract]
Line of credit facility maximum borrowing capacity				20,000,000
Line of credit facility expiration date	Sep. 30, 2013
Revolving Credit Facility [Member]
Senior Notes [Abstract]
Interest Rate (in hundredths)	0.625%
Credit facilities [Abstract]
Line of credit facility maximum borrowing capacity	750,000,000
Line of credit initiation date	Mar. 23, 2010
Interest Rate (in hundredths)	0.625%
Line of credit facility expiration date	Jan. 01, 2014
Senior Notes and Debentures [Member]
Long Term Debt [Roll Forward]
Interest Rate (in hundredths)	7.78%	[2]		7.69%	[2]
Senior Notes [Abstract]
Weighted average interest rate (in hundredths)	7.78%	[2]		7.69%	[2]
Senior Unsecured Term Loan [Member]
Credit Agreement [Abstract]
Debt instrument, face amount	575,000,000
Debt instrument, maturity date	Oct. 14, 2016
Repayment of the outstanding principal balance, quarterly installments amount	14,400,000
First payment date of the quarterly repayment of the outstanding principal balance	Mar. 31, 2012
Interest rate margin for Base Rate borrowings, minimum (in hundredths)	0.875%
Interest rate margin for Base Rate borrowings, maximum (in hundredths)	2.875%
Interest rate margin for LIBOR borrowings, minimum (in hundredths)	1.875%
Interest rate margin for LIBOR borrowings, maximum (in hundredths)	3.875%
Initial pricing for LIBOR based borrowings (in hundredths)	2.875%
Maximum permitted leverage ratio	4.5
Rural Utilities Service Loan Contracts [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance	9,322,000
Payments and Retirements	(96,000)
New Borrowings	0
Long-term debt, ending balance	9,226,000
Interest Rate (in hundredths)	6.15%	[1]
Senior Notes [Abstract]
Principal Outstanding	9,226,000
Weighted average interest rate (in hundredths)	6.15%	[1]
Senior Unsecured Debt [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance	8,919,696,000
Payments and Retirements	(517,033,000)
New Borrowings	0
Long-term debt, ending balance	8,402,663,000
Interest Rate (in hundredths)	7.95%	[1]
Senior Notes [Abstract]
Principal Outstanding	8,402,663,000
Weighted average interest rate (in hundredths)	7.95%	[1]
Senior Unsecured Debt [Member] | Senior Note Due 2/15/2028 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				200,000,000
Long-term debt, ending balance	200,000,000			200,000,000
Senior Notes [Abstract]
Principal Outstanding	200,000,000			200,000,000
Interest Rate (in hundredths)	6.73%			6.73%
Credit facilities [Abstract]
Interest Rate (in hundredths)	6.73%			6.73%
Senior Unsecured Debt [Member] | Senior Note Due 10/15/2029 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				50,000,000
Long-term debt, ending balance	50,000,000			50,000,000
Senior Notes [Abstract]
Principal Outstanding	50,000,000			50,000,000
Interest Rate (in hundredths)	8.40%			8.40%
Credit facilities [Abstract]
Interest Rate (in hundredths)	8.40%			8.40%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				8,669,696,000
Long-term debt, ending balance	8,152,663,000			8,669,696,000
Senior Notes [Abstract]
Principal Outstanding	8,152,663,000			8,669,696,000
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 1/15/2013 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				502,658,000
Long-term debt, ending balance	0			502,658,000
Senior Notes [Abstract]
Principal Outstanding	0			502,658,000
Interest Rate (in hundredths)	0.00%			6.25%
Credit facilities [Abstract]
Interest Rate (in hundredths)	0.00%			6.25%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 5/1/2014 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				200,000,000
Long-term debt, ending balance	200,000,000			200,000,000
Senior Notes [Abstract]
Principal Outstanding	200,000,000			200,000,000
Interest Rate (in hundredths)	8.25%			8.25%
Credit facilities [Abstract]
Interest Rate (in hundredths)	8.25%			8.25%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 3/15/2015 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				300,000,000	[3]
Long-term debt, ending balance	300,000,000	[3]		300,000,000	[3]
Senior Notes [Abstract]
Principal Outstanding	300,000,000	[3]		300,000,000	[3]
Interest Rate (in hundredths)	6.625%	[3]		6.625%	[3]
Credit facilities [Abstract]
Interest Rate (in hundredths)	6.625%	[3]		6.625%	[3]
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 4/15/2015 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				374,803,000	[3]
Long-term debt, ending balance	374,803,000	[3]		374,803,000	[3]
Senior Notes [Abstract]
Principal Outstanding	374,803,000	[3]		374,803,000	[3]
Interest Rate (in hundredths)	7.875%	[3]		7.875%	[3]
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.875%	[3]		7.875%	[3]
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 4/15/2017 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				1,040,685,000	[3]
Long-term debt, ending balance	1,040,685,000	[3]		1,040,685,000	[3]
Senior Notes [Abstract]
Principal Outstanding	1,040,685,000	[3]		1,040,685,000	[3]
Interest Rate (in hundredths)	8.25%	[3]		8.25%	[3]
Credit facilities [Abstract]
Interest Rate (in hundredths)	8.25%	[3]		8.25%	[3]
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 10/1/2018 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				600,000,000
Long-term debt, ending balance	600,000,000			600,000,000
Senior Notes [Abstract]
Principal Outstanding	600,000,000			600,000,000
Interest Rate (in hundredths)	8.125%			8.125%
Credit facilities [Abstract]
Interest Rate (in hundredths)	8.125%			8.125%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 1/15/2023 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				850,000,000
Long-term debt, ending balance	850,000,000			850,000,000
Senior Notes [Abstract]
Principal Outstanding	850,000,000			850,000,000
Interest Rate (in hundredths)	7.125%			7.125%
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.125%			7.125%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 3/15/2019 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				434,000,000
Long-term debt, ending balance	434,000,000			434,000,000
Senior Notes [Abstract]
Principal Outstanding	434,000,000			434,000,000
Interest Rate (in hundredths)	7.125%			7.125%
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.125%			7.125%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 4/15/2020 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				1,100,000,000
Long-term debt, ending balance	1,100,000,000			1,100,000,000
Senior Notes [Abstract]
Principal Outstanding	1,100,000,000			1,100,000,000
Interest Rate (in hundredths)	8.50%			8.50%
Credit facilities [Abstract]
Interest Rate (in hundredths)	8.50%			8.50%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 7/1/2021 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				500,000,000
Long-term debt, ending balance	500,000,000			500,000,000
Senior Notes [Abstract]
Principal Outstanding	500,000,000			500,000,000
Interest Rate (in hundredths)	9.25%			9.25%
Credit facilities [Abstract]
Interest Rate (in hundredths)	9.25%			9.25%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 4/15/2022 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				500,000,000
Long-term debt, ending balance	500,000,000			500,000,000
Senior Notes [Abstract]
Principal Outstanding	500,000,000			500,000,000
Interest Rate (in hundredths)	8.75%			8.75%
Credit facilities [Abstract]
Interest Rate (in hundredths)	8.75%			8.75%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 1/15/2027 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				345,858,000
Long-term debt, ending balance	345,858,000			345,858,000
Senior Notes [Abstract]
Principal Outstanding	345,858,000			345,858,000
Interest Rate (in hundredths)	7.875%			7.875%
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.875%			7.875%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 8/15/2031 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				945,325,000
Long-term debt, ending balance	945,325,000			945,325,000
Senior Notes [Abstract]
Principal Outstanding	945,325,000			945,325,000
Interest Rate (in hundredths)	9.00%			9.00%
Credit facilities [Abstract]
Interest Rate (in hundredths)	9.00%			9.00%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Debenture Due 11/1/2025 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				138,000,000
Long-term debt, ending balance	138,000,000			138,000,000
Senior Notes [Abstract]
Principal Outstanding	138,000,000			138,000,000
Interest Rate (in hundredths)	7.00%			7.00%
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.00%			7.00%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Debenture Due 8/15/2026 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				1,739,000
Long-term debt, ending balance	1,739,000			1,739,000
Senior Notes [Abstract]
Principal Outstanding	1,739,000			1,739,000
Interest Rate (in hundredths)	6.80%			6.80%
Credit facilities [Abstract]
Interest Rate (in hundredths)	6.80%			6.80%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Debenture Due 10/1/2034 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				628,000
Long-term debt, ending balance	628,000			628,000
Senior Notes [Abstract]
Principal Outstanding	628,000			628,000
Interest Rate (in hundredths)	7.68%			7.68%
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.68%			7.68%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Debenture Due 7/1/2035 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				125,000,000
Long-term debt, ending balance	125,000,000			125,000,000
Senior Notes [Abstract]
Principal Outstanding	125,000,000			125,000,000
Interest Rate (in hundredths)	7.45%			7.45%
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.45%			7.45%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Debenture Due 10/1/2046 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				193,500,000
Long-term debt, ending balance	193,500,000			193,500,000
Senior Notes [Abstract]
Principal Outstanding	193,500,000			193,500,000
Interest Rate (in hundredths)	7.05%			7.05%
Credit facilities [Abstract]
Interest Rate (in hundredths)	7.05%			7.05%
Senior Unsecured Debt [Member] | Senior Notes and Debentures [Member] | Senior Note Due 10/14/2016 [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance				517,500,000	[4]
Long-term debt, ending balance	503,125,000	[4]		517,500,000	[4]
Senior Notes [Abstract]
Principal Outstanding	503,125,000	[4]		517,500,000	[4]
Interest Rate (in hundredths)	3.085%	[4]		3.095%	[4]
Credit facilities [Abstract]
Interest Rate (in hundredths)	3.085%	[4]		3.095%	[4]
Industrial Development Revenue Bonds [Member]
Long Term Debt [Roll Forward]
Long-term debt, beginning balance	13,550,000
Payments and Retirements	0
New Borrowings	0
Long-term debt, ending balance	13,550,000
Interest Rate (in hundredths)	6.33%	[1]
Senior Notes [Abstract]
Principal Outstanding	$ 13,550,000
Weighted average interest rate (in hundredths)	6.33%	[1]

[1] Interest rate includes amortization of debt issuance costs and debt premiums or discounts. The interest rates at March 31, 2013 represent a weighted average of multiple issuances.

[2] Interest rate represents a weighted average of the stated interest rates of multiple issuances.

[3] See Note 18 – Subsequent Events

[4] Represents borrowings under the Credit Agreement with CoBank.