Income Taxes - Provision (Benefit) For Taxes (Details) - USD ($) $ in Millions	3 Months Ended								5 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Oct. 31, 2016
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current									$ (15)	$ 13	$ 16	$ 54
Deferred									35	8	(38)	(12)
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current									0	19	3	9
Deferred									3	0	10	(2)
Total income tax expense (benefit)	$ 6	$ 10	$ 12	$ 12	$ 4	$ (59)	$ 26	$ 20	$ 23	$ 40	$ (9)	$ 49