401(k) Plan - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Savings Plan, 401(k) Disclosure [Line Items]
401(k) Savings Plan maximum participating employees contribution rate	60.00%	60.00%	60.00%
401(k) Savings Plan employer contributon	$ 136	$ 100	$ 83

The amount of payment into the fund established for purposes of making future disbursements to the individual in accordance with the terms and understanding of the deferred compensation arrangement.

No definition available.

Name:	us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration