Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Auction Rate Securities
Fair Value Measurements [Line Items]
Level 3 Financial Instruments, asset	$ 115
Valuation Technique	Valuation Service / Broker Quotes
Unobservable Input	Broker quotes	[1]
EETC
Fair Value Measurements [Line Items]
Level 3 Financial Instruments, asset	62
Valuation Technique	Discounted Cash Flows
Unobservable Input	Structure credit risk	[2]
EETC | Structure Credit Risk | Minimum
Fair Value Measurements [Line Items]
Level 3 fair value measurements, percentage	5.00%
Convertible Debt Derivative Asset
Fair Value Measurements [Line Items]
Level 3 Financial Instruments, asset	395
Valuation Technique	Binomial Lattice Model
Unobservable Input	Expected volatility Own credit risk	[3],[4]
Convertible Debt Derivative Asset | Expected Volatility
Fair Value Measurements [Line Items]
Level 3 fair value measurements, weighted average percentage	47.00%
Convertible Debt Derivative Asset | Expected Volatility | Minimum
Fair Value Measurements [Line Items]
Level 3 fair value measurements, percentage	45.00%
Convertible Debt Derivative Asset | Expected Volatility | Maximum
Fair Value Measurements [Line Items]
Level 3 fair value measurements, percentage	60.00%
Convertible Debt Derivative Asset | Own Credit Risk | Minimum
Fair Value Measurements [Line Items]
Level 3 fair value measurements, percentage	6.00%
Convertible Debt Option Liability
Fair Value Measurements [Line Items]
Level 3 Financial Instruments, liability	$ (199)
Valuation Technique	Binomial Lattice Model
Unobservable Input	Expected volatility Own credit risk	[3],[4]
Convertible Debt Option Liability | Expected Volatility
Fair Value Measurements [Line Items]
Level 3 fair value measurements, weighted average percentage	47.00%
Convertible Debt Option Liability | Expected Volatility | Minimum
Fair Value Measurements [Line Items]
Level 3 fair value measurements, percentage	45.00%
Convertible Debt Option Liability | Expected Volatility | Maximum
Fair Value Measurements [Line Items]
Level 3 fair value measurements, percentage	60.00%
Convertible Debt Option Liability | Own Credit Risk | Minimum
Fair Value Measurements [Line Items]
Level 3 fair value measurements, percentage	6.00%

[1] Broker quotes obtained by a third-party valuation service.

[2] Represents the credit risk premium of the EETC structure above the risk-free rate that the Company has determined market participants would use in pricing the instruments.

[3] Represents the range in volatility estimates that the Company has determined market participants would use when pricing the instruments.

[4] Represents the range of Company-specific risk adjustments that the Company has determined market participants would use as a model input.