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, 2013		$ 2,257,499	$ 2,328,044	$ (258)
Cash contributions from parent	$ 267,000	267,000
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
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)
Cash contributions from parent	502,000	502,000
Net income	523,375		523,375
Cash distributions to parent	(440,000)		(440,000)
Equity interest in unrealized gain on interest rate hedge	41			41
Balance at end of period at Dec. 31, 2016	$ 6,141,269	$ 3,678,499	$ 2,462,760	$ 10