Fair Value Measurements (Fair Value Measurements, Recurring) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	$ 1,578		$ 1,148
Money Market Funds (1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	1,036	[1]	805	[1]
Time Deposits (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	95	[2]	132	[2]
Repurchase Agreements (2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	447	[2]	211	[2]
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	1,483		1,016
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	1,036	[1]	805	[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	447	[2]	211	[2]
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash Equivalents, Fair Value	95		132
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	95	[2]	132	[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, 2013 and 2012. 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.