Trade Accounts Receivable (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012
Components of trade accounts receivable, net
Accounts receivable - billed	$ 727	$ 812
Accounts receivable - unbilled	69	80
Other receivables	13	26
Less: Allowances	(23)	(16)
Trade accounts receivable, net	$ 786	$ 902