Composition of Investments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	$ 4,505	$ 2,191
Available For Sale Securities Unrealized Gains	6	10
Available For Sale Securities Unrealized Losses	(3)	(1)
Available For Sale Securities Fair Value	4,508	2,200
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	10,190	6,535
Available For Sale Securities Unrealized Gains	37	66
Available For Sale Securities Unrealized Losses	(22)	(6)
Available For Sale Securities Fair Value	10,205	6,595
Publicly Traded Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	78	47
Available For Sale Securities Unrealized Gains	28	41
Available For Sale Securities Unrealized Losses	0	(1)
Available For Sale Securities Fair Value	106	87
Debt and Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	10,268	6,582
Available For Sale Securities Unrealized Gains	65	107
Available For Sale Securities Unrealized Losses	(22)	(7)
Available For Sale Securities Fair Value	10,311	6,682
US Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	2,106	1,480
Available For Sale Securities Unrealized Gains	6	10
Available For Sale Securities Unrealized Losses	(3)	0
Available For Sale Securities Fair Value	2,109	1,490
High Yield Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	526	486
Available For Sale Securities Unrealized Gains	17	34
Available For Sale Securities Unrealized Losses	(7)	(1)
Available For Sale Securities Fair Value	536	519
Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	5	2
Available For Sale Securities Unrealized Gains	0	0
Available For Sale Securities Unrealized Losses	0	0
Available For Sale Securities Fair Value	5	2
Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	939	1,032
Available For Sale Securities Unrealized Gains	3	3
Available For Sale Securities Unrealized Losses	(1)	0
Available For Sale Securities Fair Value	941	1,035
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	72	74
Available For Sale Securities Unrealized Gains	0	0
Available For Sale Securities Unrealized Losses	(5)	(4)
Available For Sale Securities Fair Value	67	70
Foreign Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	2,037	1,270
Available For Sale Securities Unrealized Gains	5	9
Available For Sale Securities Unrealized Losses	(3)	0
Available For Sale Securities Fair Value	$ 2,039	$ 1,279

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Publisher FASB

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

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-Name FASB Staff Position (FSP)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details