Financial Instruments (Estimated Fair Value of Debt, Financing and Capital Lease Obligations) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current and long-term debt, carrying amount	$ 33,645	$ 33,245
Current and long-term debt, total estimated fair value	28,361	33,554
Quoted prices in active markets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current and long-term debt, total estimated fair value	21,757	27,238
Observable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current and long-term debt, total estimated fair value	4,474	4,906
Unobservable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current and long-term debt, total estimated fair value	$ 2,130	$ 1,410