Investments - Gross Unrealized Losses and Fair Value of the Company's Investments (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Investments
Securities continuous unrealized losses less than 12 months - fair value	$ 7	$ 33
Securities continuous unrealized losses less than 12 months - Unrealized Losses	3	19
Securities continuous unrealized losses greater than 12 months - fair value	7	6
Securities continuous unrealized losses greater than 12 months - Unrealized Losses	1	2
Total Fair Value	14	39
Total Unrealized Loss	4	21
Marketable Equity Securities
Investments
Securities continuous unrealized losses less than 12 months - fair value	7	33
Securities continuous unrealized losses less than 12 months - Unrealized Losses	3	19
Total Fair Value	7	33
Total Unrealized Loss	3	19
Auction rate securities
Investments
Securities continuous unrealized losses greater than 12 months - fair value	7	6
Securities continuous unrealized losses greater than 12 months - Unrealized Losses	1	2
Total Fair Value	7	6
Total Unrealized Loss	$ 1	$ 2