Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Derivative Instruments And Hedging Activities [Line Items]
Estimated amount reclassified from other comprehensive income to interest expense	$ 126
Estimated termination value if there is breach of provision related to derivative agreement	$ 471

The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

No definition available.

Name:	us-gaap_DerivativeInstrumentsGainLossReclassificationFromAccumulatedOCIToIncomeEstimatedNetAmountToBeTransferred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration