Condensed Consolidated Statement of Member's Equity (Unaudited) - USD ($) $ in Thousands	Total	Member Units [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
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	551,636		551,636
Cash distributions to parent	(290,000)		(290,000)
Other comprehensive income (loss)	572			572
Balance at end of period at Sep. 30, 2018	6,539,532	4,428,499	2,110,124	909
Balance at beginning of period at Jun. 30, 2018		4,428,499	2,030,626	861
Cash contributions from parent		0
Net Income	179,498		179,498
Cash distributions to parent			(100,000)
Other comprehensive income (loss)	48			48
Balance at end of period at Sep. 30, 2018	6,539,532	4,428,499	2,110,124	909
Balance at beginning of period at Dec. 31, 2018	6,528,600	4,428,499	2,099,567	534
Cash contributions from parent	0	0
Net Income	715,883		715,883
Cash distributions to parent	(559,000)		(559,000)
Other comprehensive income (loss)	(692)			(692)
Balance at end of period at Sep. 30, 2019	6,684,791	4,428,499	2,256,450	(158)
Balance at beginning of period at Jun. 30, 2019		4,428,499	2,195,168	(65)
Cash contributions from parent		0
Net Income	274,282		274,282
Cash distributions to parent			(213,000)
Other comprehensive income (loss)	(93)			(93)
Balance at end of period at Sep. 30, 2019	$ 6,684,791	$ 4,428,499	$ 2,256,450	$ (158)