Cash, Cash Equivalents, and Marketable Securities - Summary of Contractual Maturities of Cash Equivalent and Marketable Fixed Income Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	$ 6,093
Estimated Fair Value	6,097
Due within one year
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	3,951
Estimated Fair Value	3,953
Due after one year through five years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	1,781
Estimated Fair Value	1,784
Due after five years through ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	129
Estimated Fair Value	129
Due after ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	232
Estimated Fair Value	$ 231