Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Mar. 31, 2015		Dec. 31, 2014	Mar. 31, 2014
Financial Instruments
Cash and Cash Equivalents, at Carrying Value	$ 2,263	$ 2,068	[1]	$ 2,166	$ 1,782

[1] Derived from audited Consolidated Financial Statements.