Income Taxes - Operating Loss and Tax Credit Carryforwards (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 15	$ 25
Net operating loss carryforward with no expiration	3	0
Net operating loss carryforward with expiration	12	25
Tax credit carryforwards	9	0
Tax credit carryforwards with no expiration	0	0
Tax credit carryforwards with expiration	9	0
Capital loss carryforwards	0	0
Capital loss carryforwards with no expiration	0	0
Capital loss carryforwards with expiration	0	0
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	673	845
Net operating loss carryforward with no expiration	6	9
Net operating loss carryforward with expiration	667	836
Tax credit carryforwards	16	23
Tax credit carryforwards with no expiration	7	7
Tax credit carryforwards with expiration	9	16
Capital loss carryforwards	0	0
Capital loss carryforwards with no expiration	0	0
Capital loss carryforwards with expiration	0	0
Foreign
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	10,512	7,595
Net operating loss carryforward with no expiration	6,471	7,292
Net operating loss carryforward with expiration	4,041	303
Tax credit carryforwards	16	18
Tax credit carryforwards with no expiration	0	0
Tax credit carryforwards with expiration	16	18
Capital loss carryforwards	59	236
Capital loss carryforwards with no expiration	40	211
Capital loss carryforwards with expiration	$ 19	$ 25