Consolidated Statements of Changes in Common Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Retained Earnings	AOCI	Noncontrolling Interest
Beginning balance at Dec. 31, 2019	$ 3,892	$ 3,695	$ 20	$ (3)	$ 180
Beginning balance (in shares) at Dec. 31, 2019		40
Total comprehensive income (loss) available(attributable) to common shareholder	266		258		8
Capital contribution from parent	322	$ 322
Ending balance at Sep. 30, 2020	4,480	$ 4,017	278	(3)	188
Ending balance (in shares) at Sep. 30, 2020		40
Beginning balance at Jun. 30, 2020	4,052	$ 3,695	177	(3)	183
Beginning balance (in shares) at Jun. 30, 2020		40
Total comprehensive income (loss) available(attributable) to common shareholder	106		101		5
Capital contribution from parent	322	$ 322
Ending balance at Sep. 30, 2020	4,480	$ 4,017	278	(3)	188
Ending balance (in shares) at Sep. 30, 2020		40
Beginning balance at Dec. 31, 2020	4,484	$ 4,017	277	(2)	192
Beginning balance (in shares) at Dec. 31, 2020		40
Total comprehensive income (loss) available(attributable) to common shareholder	77		64		13
Capital contribution from parent	149	$ 149
Dividend to parent	(180)		(150)		(30)
Ending balance at Sep. 30, 2021	4,530	$ 4,166	191	(2)	175
Ending balance (in shares) at Sep. 30, 2021		40
Beginning balance at Jun. 30, 2021	4,308	$ 4,017	122	(2)	171
Beginning balance (in shares) at Jun. 30, 2021		40
Total comprehensive income (loss) available(attributable) to common shareholder	148		144		4
Capital contribution from parent	149	$ 149
Dividend to parent	(75)		(75)
Ending balance at Sep. 30, 2021	$ 4,530	$ 4,166	$ 191	$ (2)	$ 175
Ending balance (in shares) at Sep. 30, 2021		40