Income Taxes - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Line Items]
Provision for income taxes at U.S. federal statutory tax rate	35.00%	21.00%	21.00%	31.60%
Income tax benefit attributable to revaluation of net deferred tax liabilities				$ 2,900,000,000
Federal tax credits for alternative fuel vehicles and plug-in vehicles		$ 52,000,000	$ 38,000,000
Tax credits for research and development		10,000,000	14,000,000
Tax credits for foreign tax		1,000,000	3,000,000
Tax credits for alternative minimum tax			12,000,000
Valuation Allowance		13,000,000	24,000,000
Unremitted earnings in foreign subsidiary		243,000,000	233,000,000
Income tax payable		47,000,000
Unrecognized tax benefits would effect on effective tax rate		17,000,000	6,000,000	6,000,000
Increase in unrecognized tax benefits		11,000,000
Income Tax Penalties Accrued		0	0	$ 0
Federal [Member]
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards		$ 0	2,100,000,000
Tax credit carryforward, Expiration Date		Mar. 31, 2028
State [Member]
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards		$ 37,000,000	$ 147,000,000
Expiration Dates		Mar. 31, 2022