Income Taxes - Operating Loss and Tax Credit Carryforwards (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 25	$ 41
Net operating loss carryforward with no expiration	0	0
Net operating loss carryforward with expiration	25	41
Tax credit carryforwards	0	0
Tax credit carryforwards with no expiration	0	0
Tax credit carryforwards with expiration	0	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	845	873
Net operating loss carryforward with no expiration	9	0
Net operating loss carryforward with expiration	836	873
Tax credit carryforwards	23	28
Tax credit carryforwards with no expiration	7	7
Tax credit carryforwards with expiration	16	21
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	7,595	6,522
Net operating loss carryforward with no expiration	7,292	6,287
Net operating loss carryforward with expiration	303	235
Tax credit carryforwards	18	21
Tax credit carryforwards with no expiration	0	0
Tax credit carryforwards with expiration	18	21
Capital loss carryforwards	236	240
Capital loss carryforwards with no expiration	211	193
Capital loss carryforwards with expiration	$ 25	$ 47