Consolidation (Details) - USD ($) $ in Millions	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Current assets
Cash and cash equivalents	$ 594	$ 556	$ 628	$ 509
Inventories	1,333	1,180
Prepaid expenses and other current assets	111	127
Total current assets	3,281	2,971
Property, plant and equipment, net	3,357	3,506
Goodwill	607	607
Deferred income taxes	82	87
Other long-term assets	94	82
Total assets	8,344	8,280
Current liabilities
Accounts payable	1,722	1,506
Accrued expenses and other current liabilities	554	569
Total current liabilities	2,893	2,834
Accrued postretirement benefits	799	820
Other long–term liabilities	198	175
Total liabilities	8,421	8,339
Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents	2	3
Accounts receivable	29	33
Inventories	62	61
Prepaid expenses and other current assets	2	2
Property, plant and equipment, net	25	21
Goodwill	12	12
Deferred income taxes	89	84
Other long-term assets	30	8
Current liabilities
Accounts payable	32	30
Accrued expenses and other current liabilities	21	15
Accrued postretirement benefits	224	214
Other long–term liabilities	3	3
Logan [Member]
Current assets
Total current assets	95	99
Total assets	251	224
Current liabilities
Total current liabilities	53	45
Total liabilities	$ 280	$ 262