Other Assets - Changes in the carrying amount of Goodwill (Details) - USD ($) $ in Millions	5 Months Ended	7 Months Ended	12 Months Ended
	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Balance - beginning of period(1)	$ 10
Addition from acquisitions	13
Goodwill disposition	0
Balance - end of period	23	$ 10	$ 23
Predecessor
Goodwill [Roll Forward]
Balance - beginning of period(1)	$ 72	72	$ 72	$ 74
Addition from acquisitions		0		0
Goodwill disposition		0		(2)
Balance - end of period		$ 72		$ 72