Fair Value Measurements (Fair Value Measurements, Recurring) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	$ 4,217		$ 2,865
Money Market Funds (1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	2,880	[1]	2,284	[1]
Time Deposits (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	94	[2]	12	[2]
Repurchase Agreements (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	1,243	[2]	569	[2]
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	4,123		2,853
Fair Value, Inputs, Level 1 [Member] | Money Market Funds (1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	2,880	[1]	2,284	[1]
Fair Value, Inputs, Level 1 [Member] | Time Deposits (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	0	[2]	0	[2]
Fair Value, Inputs, Level 1 [Member] | Repurchase Agreements (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	1,243	[2]	569	[2]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	94		12
Fair Value, Inputs, Level 2 [Member] | Money Market Funds (1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	0	[1]	0	[1]
Fair Value, Inputs, Level 2 [Member] | Time Deposits (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	94	[2]	12	[2]
Fair Value, Inputs, Level 2 [Member] | Repurchase Agreements (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	0	[2]	0	[2]
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	0		0
Fair Value, Inputs, Level 3 [Member] | Money Market Funds (1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	0	[1]	0	[1]
Fair Value, Inputs, Level 3 [Member] | Time Deposits (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	0	[2]	0	[2]
Fair Value, Inputs, Level 3 [Member] | Repurchase Agreements (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	$ 0	[2]	$ 0	[2]

[1] Gross unrealized gain and losses were not material for the years ended March 31, 2015 and 2014 based on quoted prices of identical investments.

[2] The carrying amounts of these cash equivalents approximated their estimated fair values because of their short maturities.