Income Taxes (Narrative) (Details) (USD $)	12 Months Ended				12 Months Ended	3 Months Ended	9 Months Ended					12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2014 Internal Revenue Service (IRS) [Member]	Dec. 31, 2013 Canada Revenue Agency Assessments [Member]	Dec. 31, 2013 Canada Revenue Agency Assessments [Member]	Mar. 31, 2014 State and Local Jurisdiction [Member]	Mar. 31, 2014 Domestic Tax Authority [Member]	Mar. 31, 2014 Foreign Tax Authority [Member]	Mar. 31, 2014 Foreign Tax Authority [Member] Research Tax Credit Carryforward [Member]	Mar. 31, 2012 Average Wholesale Price Litigation [Member]
Income Tax [Line Items]
Income Tax Expense Discrete Items	$ (94,000,000)	$ 29,000,000	$ 66,000,000			$ 122,000,000						$ 31,000,000
Tax assessments received relating to transfer pricing issues					98,000,000		219,000,000
Undistributed Earnings of Foreign Operations	4,200,000,000
Federal, State and Foreign Operating Loss Carryforwards								2,524,000,000	53,000,000	935,000,000
Canadian research and development carryforwards											11,000,000
Unrecognized Tax Benefits	647,000,000	560,000,000	595,000,000	635,000,000
Unrecognized Tax Benefits that would Impact Income Tax Expense and the Effective Tax Rate	490,000,000
Potential Reduction of Unrecognized Benefits Due to Audit Resolutions and Expiration of Statutes of Limitations	230,000,000
Income Tax Expense, Before Any Tax Effect, Related to Accrued Interest Expense	48,000,000
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount	8,000,000
Accrued interest and penalties on unrecognized tax benefits	179,000,000	131,000,000
Deferred Tax Liabilities, Undistributed Foreign Earnings	$ 0