Fair Value Hierarchy For Financial Assets And Liabilities Measured At Fair Value (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Percentage of Loans Guaranteed	95.00%
Total cash and investments	$ 15,261	$ 17,588
Investment in joint venture, fair value	35	35
Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	59	60
Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	7,316	8,237
Investment in joint venture, fair value	0	0
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	7,886	9,291
Investment in joint venture, fair value	0	0
Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	4,584	6,166
Cash Equivalents | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Cash Equivalents | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	320	492
Cash Equivalents | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	4,264	5,674
Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,707	1,725
Cash | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Cash | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Cash | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,707	1,725
Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt		(5,419)
Convertible Debt | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt		0
Convertible Debt | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt		(5,419)
Convertible Debt | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Convertible debt
Long-term Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	5,496
Long-term Debt | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	0
Long-term Debt | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	(5,496)
Long-term Debt | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt	0
Private Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	384	379
Private Equity Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	384	379
Private Equity Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Private Equity Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Publicly Traded Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	119	95
Publicly Traded Equity Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Publicly Traded Equity Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Publicly Traded Equity Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	119	95
Foreign Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	2,298	2,155
Foreign Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Foreign Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	2,298	2,155
Foreign Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Auction Rate Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	59	60
Auction Rate Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	59	60
Auction Rate Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Auction Rate Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Municipal Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	828	863
Municipal Obligations | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
Municipal Obligations | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	828	863
Municipal Obligations | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
High Yield Corporate Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	565	531
High Yield Corporate Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
High Yield Corporate Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	565	531
High Yield Corporate Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Corporate Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	2,356	2,266
US Corporate Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Corporate Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	2,356	2,266
US Corporate Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Government Agencies Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	2,745	3,727
US Government Agencies Debt Securities | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments
US Government Agencies Debt Securities | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	949	1,930
US Government Agencies Debt Securities | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and investments	1,796	1,797
Foreign Exchange Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets	21	31
Foreign exchange derivative liabilities	(18)	(20)
Foreign Exchange Contract | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets		0
Foreign exchange derivative liabilities		0
Foreign Exchange Contract | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets	21	31
Foreign exchange derivative liabilities	(18)	(20)
Foreign Exchange Contract | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Foreign exchange derivative assets
Foreign exchange derivative liabilities
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities	1	4
Commodity Contract | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities		0
Commodity Contract | Fair Value, Inputs, Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities	1	4
Commodity Contract | Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative liabilities