CONSOLIDATED STATEMENTS OF CAPITALIZATION (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Long-Term Debt
Unamortized discount	$ (9,468)		$ (8,349)
Total long-term debt	3,630,773		3,486,275
Long-term debt, current maturities	256,297		605,633
Total long-term debt, noncurrent	3,374,476		2,880,642
Common Stockholder's Equity
Common stock - 100 shares authorized of $0.01 par value, 100 shares outstanding at Dec. 31, 2012 and 2011, respectively	0		0
Additional paid in capital	3,415,669		3,316,386
Retained earnings	1,192,937		1,001,709
Accumulated other comprehensive loss	(22,871)		(12,377)
Total common stockholder's equity	4,585,735		4,305,718
First Mortgage Bonds [Member] | Series Due Oct. 1, 2012 [Member]
Long-Term Debt
Long-term debt, gross	0		600,000
First Mortgage Bonds [Member] | Series Due March 1, 2013 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
First Mortgage Bonds [Member] | Series Due April 1, 2014 [Member]
Long-Term Debt
Long-term debt, gross	275,000		275,000
First Mortgage Bonds [Member] | Series Due Sept. 1, 2017 [Member]
Long-Term Debt
Long-term debt, gross	129,500	[1]	129,500	[1]
First Mortgage Bonds [Member] | Series Due Aug. 1, 2018 [Member]
Long-Term Debt
Long-term debt, gross	300,000		300,000
First Mortgage Bonds [Member] | Series Due Jan. 1, 2019 [Member]
Long-Term Debt
Long-term debt, gross	0	[1]	48,750	[1]
First Mortgage Bonds [Member] | Series Due June 1, 2019 [Member]
Long-Term Debt
Long-term debt, gross	400,000		400,000
First Mortgage Bonds [Member] | Series Due Nov. 15, 2020 [Member]
Long-Term Debt
Long-term debt, gross	400,000		400,000
First Mortgage Bonds [Member] | Series Due Sept. 15, 2022 [Member]
Long-Term Debt
Long-term debt, gross	300,000		0
First Mortgage Bonds [Member] | Series Due Sept. 1, 2037 [Member]
Long-Term Debt
Long-term debt, gross	350,000		350,000
First Mortgage Bonds [Member] | Series Due Aug. 1, 2038 [Member]
Long-Term Debt
Long-term debt, gross	300,000		300,000
First Mortgage Bonds [Member] | Series Due Aug. 15, 2041 [Member]
Long-Term Debt
Long-term debt, gross	250,000		250,000
First Mortgage Bonds [Member] | Series Due Sept. 15, 2042 [Member]
Long-Term Debt
Long-term debt, gross	500,000		0
Capital Lease Obligations [Member]
Long-Term Debt
Capital lease obligations	$ 185,741		$ 191,374

[1] Pollution control financing