Consolidated Statement of Owner's Equity Consolidated Statement of Owner's Equity (USD $) In Thousands	Total	Member's Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of period at Dec. 31, 2011		$ 1,841,888	$ 2,177,811	$ (346)
Cash contributions from parent	150,000	150,000
Non-cash contributions from parent	1,500	1,524
Net income	272,466		272,466
Cash distributions to parent	(246,259)		(246,259)
Equity interest in unrealized gain (loss) on interest rate hedge	(376)			(376)
Balance at end of period at Dec. 31, 2012	4,196,708	1,993,412	2,204,018	(722)
Cash contributions from parent	264,000	264,000
Non-cash contributions from parent		87
Net income	374,026		374,026
Cash distributions to parent	(250,000)		(250,000)
Equity interest in unrealized gain (loss) on interest rate hedge	464			464
Balance at end of period at Dec. 31, 2013	4,585,285	2,257,499	2,328,044	(258)
Cash contributions from parent	267,000	267,000
Non-cash contributions from parent		0
Net income	422,884		422,884
Cash distributions to parent	(411,000)		(411,000)
Equity interest in unrealized gain (loss) on interest rate hedge	143			143
Balance at end of period at Dec. 31, 2014	$ 4,864,312	$ 2,524,499	$ 2,339,928	$ (115)