Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Deferred tax assets
Employee benefits	$ 0	$ 79
Tax loss/credit carryforwards	2,516	1,917
Accrued interest	12	16
Operating lease liabilities	370	0
Contract accounting	126	130
Other assets	144	139
Total deferred tax assets	3,168	2,281
Valuation allowance	(2,162)	(1,575)
Net deferred tax assets	1,006	706
Deferred tax liabilities
Depreciation and amortization	(850)	(994)
Operating right-of-use asset	(343)	0
Investment basis differences	(68)	(61)
Employee benefits	(48)	0
Other liabilities	(150)	(63)
Total deferred tax liabilities	(1,459)	(1,118)
Total net deferred tax assets (liabilities)	$ (453)	$ (412)