Shareholders' Equity (Details) (USD $) In Billions, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Shareholders' Equity
Maximum expenditure authorized for repurchase of common stock	$ 2.0

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