Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018
Deferred tax assets
Employee benefits	$ 79	$ 156
Tax loss/credit carryforwards	1,917	1,665
Accrued interest	16	18
Contract accounting	130	134
Other assets	139	232
Total deferred tax assets	2,281	2,205
Valuation allowance	(1,575)	(1,440)
Net deferred tax assets	706	765
Deferred tax liabilities
Depreciation and amortization	(994)	(888)
Investment basis differences	(61)	(62)
Other liabilities	(63)	(94)
Total deferred tax liabilities	(1,118)	(1,044)
Total net deferred tax assets (liabilities)	$ (412)	$ (279)