Common Stock (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012
Common Stock [Abstract]
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 553

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

No definition available.

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