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, 2012		$ 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 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 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)
Cash contributions from parent	652,000	652,000
Non-cash contributions from parent		0
Net income	575,457		575,457
Cash distributions to parent	(536,000)		(536,000)
Equity interest in unrealized gain on interest rate hedge	84			84
Balance at end of period at Dec. 31, 2015	$ 5,555,853	$ 3,176,499	$ 2,379,385	$ (31)