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	Dec. 31, 2013
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	$ 9,735
Estimated Fair Value	9,736
Due within one year
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	7,226
Estimated Fair Value	7,227
Due after one year through five years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	2,115
Estimated Fair Value	2,118
Due after five years through ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	133
Estimated Fair Value	132
Due after ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	261
Estimated Fair Value	$ 259