Subsequent Events (Details) (Stock Repurchase Plan, USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended
Apr. 19, 2012	Mar. 31, 2012
Stock Repurchase Plan
Subsequent Event [Line Items]
Total repurchase amount authorized	$ 680	$ 500

The amount authorized by an entity's Board of Directors under a stock repurchase plan.

No definition available.

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