Related Party Transactions - Schedule of Condensed Combined Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2017
Related Party Transactions [Abstract]
Allocated operating expenses	$ 16	$ 3	$ 20	$ 8
Maintenance service costs	3	0	3	0
Insurance expense	5	5	10	9
Other	8	8	13	13
Operations and maintenance – related parties	32	16	46	30	$ 30
Allocated general corporate expenses	10	8	17	14
Management Agreement fee	3	2	5	4
Omnibus Agreement fee	2	2	5	5
Other	2	0	2	0
General and administrative – related parties	$ 17	$ 12	$ 29	$ 23