Consolidation (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Current assets
Cash and cash equivalents	$ 628	$ 509	$ 301	$ 317
Inventories	1,431	1,173
Prepaid expenses and other current assets	112	101
Total current assets	3,675	3,473
Property, plant and equipment, net	3,542	3,513
Goodwill	607	611
Deferred income taxes	95	80
Other long-term assets	137	173
Total assets	9,102	9,114
Current liabilities
Accounts payable	1,854	1,418
Accrued expenses and other current liabilities	572	547
Total current liabilities	3,593	3,170
Accrued postretirement benefits	748	621
Other long–term liabilities	221	271
Total liabilities	9,172	8,846
Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents	2	1
Accounts receivable	40	38
Inventories	52	42
Prepaid expenses and other current assets	1	1
Property, plant and equipment, net	20	14
Goodwill	12	12
Deferred income taxes	65	63
Other long-term assets	4	3
Current liabilities
Accounts payable	33	26
Accrued expenses and other current liabilities	12	13
Accrued postretirement benefits	166	141
Other long–term liabilities	2	2
Logan [Member]
Current assets
Total current assets	95	82
Total assets	196	174
Current liabilities
Total current liabilities	45	39
Total liabilities	$ 213	$ 182