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, 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	159		150		9
Capital contribution from parent	20				20
Dividend to parent	(74)		(72)		(2)
Ending balance at Jun. 30, 2018	5,085	$ 2,860	2,060	(4)	169
Ending balance (in shares) at Jun. 30, 2018		40
Beginning balance at Mar. 31, 2018	5,034	$ 2,860	2,034	(4)	144
Beginning balance (in shares) at Mar. 31, 2018		40
Total comprehensive income (loss) available (attributable) to common shareholder	31		26		5
Capital contribution from parent	20				20
Ending balance at Jun. 30, 2018	5,085	$ 2,860	2,060	(4)	169
Ending balance (in shares) at Jun. 30, 2018		40
Beginning balance at Dec. 31, 2018	4,315	$ 2,860	1,279	(3)	179
Beginning balance (in shares) at Dec. 31, 2018		40
Cumulative-effect of change in accounting principle	0		1	(1)
Total comprehensive income (loss) available (attributable) to common shareholder	(1,173)		(1,187)		14
Capital contribution from parent	775	$ 775
Capital contribution returned to parent	(20)				(20)
Dividend to parent	(20)		(20)
Other	(1)		(1)
Ending balance at Jun. 30, 2019	3,876	$ 3,635	72	(4)	173
Ending balance (in shares) at Jun. 30, 2019		40
Beginning balance at Mar. 31, 2019	3,867	$ 3,535	151	(4)	185
Beginning balance (in shares) at Mar. 31, 2019		40
Total comprehensive income (loss) available (attributable) to common shareholder	(70)		(78)		8
Capital contribution from parent	100	$ 100
Capital contribution returned to parent	(20)				(20)
Other	(1)		(1)
Ending balance at Jun. 30, 2019	$ 3,876	$ 3,635	$ 72	$ (4)	$ 173
Ending balance (in shares) at Jun. 30, 2019		40