Equity (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		6 Months Ended
	Jun. 30, 2019	Feb. 28, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Stockholders Equity Note [Abstract]
Common stock, par value	$ 0		$ 0
Common stock, shares authorized	50,000,000		50,000,000
Shares, issued	40,300,000		40,300,000
Common stock, shares outstanding	40,300,000		40,300,000		40,300,000
Preferred stock, par value	$ 0		$ 0
Preferred stock, shares authorized	20,000,000		20,000,000
Preferred stock, shares issued	1,000		1,000
Preferred stock, shares outstanding	1,000		1,000
Contributions from parent	$ 100	$ 675	$ 775	$ 20
Retained earnings, restricted	$ 126		$ 126		$ 115