Income Taxes - Provision (Benefit) For Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current									$ (14)	$ 13	$ 16
Deferred									(30)	8	(38)
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current									15	19	3
Deferred									(25)	0	10
Total income tax expense (benefit)	$ (95)	$ 22	$ 8	$ 11	$ 6	$ 10	$ 12	$ 12	$ (54)	$ 40	$ (9)