Consolidated Statement of Member's Equity Consolidated Statement of Member's Equity - USD ($) $ in Thousands	Total	Member's Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of period at Dec. 31, 2017		$ 4,088,499	$ 1,848,488	$ 337
Cash contributions from parent	$ 340,000	340,000
Net income	741,079		741,079
Cash distributions to parent	(490,000)		(490,000)
Non-cash distribution to parent			0
Non-cash distribution of investments in subsidiaries			0	0
Equity interest in unrealized gain (loss) on interest rate hedge	197			197
Balance at end of period at Dec. 31, 2018	6,528,600	4,428,499	2,099,567	534
Cash contributions from parent	0	0
Net income	963,296		963,296
Cash distributions to parent	(824,000)		(824,000)
Non-cash distribution to parent			(25,000)
Non-cash distribution of investments in subsidiaries			(36,579)	(107)
Equity interest in unrealized gain (loss) on interest rate hedge	(641)			(641)
Balance at end of period at Dec. 31, 2019	6,605,783	4,428,499	2,177,284	0
Cash contributions from parent	115,000	115,000
Net income	880,036		880,036
Cash distributions to parent	(1,020,000)		(1,020,000)
Non-cash distribution to parent			0
Non-cash distribution of investments in subsidiaries			0	0
Equity interest in unrealized gain (loss) on interest rate hedge	0			0
Balance at end of period at Dec. 31, 2020	$ 6,580,819	$ 4,543,499	$ 2,037,320	$ 0