Consolidation (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2013
Current assets
Cash and cash equivalents	$ 326	$ 509	$ 338	$ 301
Inventories	1,504	1,173
Prepaid expenses and other current assets	124	101
Total current assets	3,760	3,473
Property, plant and equipment, net	3,535	3,513
Goodwill	608	611
Deferred income taxes	77	80
Other long-term assets	160	173
Total assets	9,321	9,114
Current liabilities
Accounts payable	1,643	1,418
— third parties	556	547
Total current liabilities	3,532	3,170
Accrued postretirement benefits	612	621
Other long–term liabilities	256	271
Total liabilities	9,084	8,846
Variable Interest Entity, Primary Beneficiary [Member]
Current assets
Cash and cash equivalents	3	1
Accounts receivable - third parties	28	38
Inventories	50	42
Prepaid expenses and other current assets	1	1
Total current assets	82	82
Property, plant and equipment, net	13	14
Goodwill	12	12
Deferred income taxes	66	63
Other long-term assets	3	3
Total assets	176	174
Current liabilities
Accounts payable	23	26
— third parties	13	13
Total current liabilities	36	39
Accrued postretirement benefits	146	141
Other long–term liabilities	2	2
Total liabilities	$ 184	$ 182