Fair Value of Financial Assets and Liabilities - Composition of Investments (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
U.S. government and agency obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 2,258	$ 1,951
Unrealized Gains	3	2
Unrealized (Losses)	(2)	(2)
Aggregate Fair Value	2,259	1,951
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,421	1,998
Unrealized Gains	3	1
Unrealized (Losses)	(7)	(4)
Aggregate Fair Value	2,417	1,995
High yield corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	398	570
Unrealized Gains	5	9
Unrealized (Losses)	(9)	(16)
Aggregate Fair Value	394	563
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	36	53
Unrealized Gains	0	0
Unrealized (Losses)	0	0
Aggregate Fair Value	36	53
Municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	916	948
Unrealized Gains	1	2
Unrealized (Losses)	0	0
Aggregate Fair Value	917	950
Auction rate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27	29
Unrealized Gains	0	0
Unrealized (Losses)	(1)	(2)
Aggregate Fair Value	26	27
Foreign debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,658	2,566
Unrealized Gains	2	2
Unrealized (Losses)	(3)	(4)
Aggregate Fair Value	2,657	2,564
Fixed income securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,714	8,115
Unrealized Gains	14	16
Unrealized (Losses)	(22)	(28)
Aggregate Fair Value	8,706	8,103
Publicly traded equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	187	117
Unrealized Gains	95	103
Unrealized (Losses)	(8)	(11)
Aggregate Fair Value	274	209
Fixed income and publicly traded equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,901	8,232
Unrealized Gains	109	119
Unrealized (Losses)	(30)	(39)
Aggregate Fair Value	$ 8,980	$ 8,312

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Name Accounting Standards Codification

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