Income Taxes (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Income Tax Disclosure [Line Items]      
Repatriation of Certain Wholly-Owned Subsidiaries   $ 700  
Tax Benefits Allocated Directly to Contributed Capital 21 12  
Valuation allowance decrease 120    
Gross unrecognized tax benefits 254 232 297
Amount of unrecognized tax benefits that would affect the effective tax rate 58 84  
The total amount of unrecognized tax benefits that, if recognized, would result in adjustments to deferred tax assets with corresponding 195 148  
Combined amount of accrued interest and penalties related to uncertain tax positions 16 16  
Amount of unrecognized tax benefits for which it is reasonably possible that there will be a reduction within the next 12 months 11    
Internal Revenue Service (IRS) [Member]      
Income Tax Disclosure [Line Items]      
Tax credit carry forwards 320    
Tax credit carryforward, expiration dates Jan. 01, 2024    
Foreign Country [Member]      
Income Tax Disclosure [Line Items]      
Undistributed Earnings of Foreign Subsidiaries 752    
Tax credit carry forwards 7    
State [Member]      
Income Tax Disclosure [Line Items]      
Net operating Loss Carryforwards 785    
Net operating loss attributable to various acquired companies 114    
Operating loss carryforwards, expiration dates Jan. 01, 2016    
Tax credit carry forwards $ 131