Consolidated Statements of Changes in Common Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjustment	Noncontrolling Interest
Beginning balance at Dec. 31, 2017	$ 4,980	$ 2,860	$ 1,982		$ (4)		$ 142
Beginning balance (in shares) at Dec. 31, 2017		40
Total comprehensive income (loss) available (attributable) to common shareholder	(588)		(614)		1		25
Capital contribution from parent	24						24
Dividend to parent	(101)		(89)				(12)
Ending balance at Dec. 31, 2018	4,315	$ 2,860	1,279	$ 1	(3)	$ (1)	179
Ending balance (in shares) at Dec. 31, 2018		40
Total comprehensive income (loss) available (attributable) to common shareholder	(1,221)		(1,240)		1		18
Capital contribution from parent	838	$ 835					3
Capital contribution returned to parent	(20)						(20)
Dividend to parent	(20)		(20)
Ending balance at Dec. 31, 2019	3,892	$ 3,695	20		(3)		180
Ending balance (in shares) at Dec. 31, 2019		40
Total comprehensive income (loss) available (attributable) to common shareholder	308		295		1		12
Capital contribution from parent	322	$ 322
Dividend to parent	(38)		(38)
Ending balance at Dec. 31, 2020	$ 4,484	$ 4,017	$ 277		$ (2)		$ 192
Ending balance (in shares) at Dec. 31, 2020		40