Cash, Cash Equivalents, and Marketable Securities - Summary of Contractual Maturities of Cash Equivalent and Marketable Fixed Income Securities (Detail) $ in Millions	Dec. 31, 2015 USD ($)
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	$ 13,884
Estimated Fair Value	13,877
Due within one year
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	12,533
Estimated Fair Value	12,531
Due after one year through five years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	1,086
Estimated Fair Value	1,084
Due after five years through ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	96
Estimated Fair Value	95
Due after ten years
Investments Classified by Contractual Maturity Date [Line Items]
Amortized Cost	169
Estimated Fair Value	$ 167