Subsequent Event (Details) (Common Stock, USD $) In Millions, unless otherwise specified	1 Months Ended
Dec. 30, 2011	Aug. 31, 2012 Subsequent event Stock repurchases
Subsequent event
Common stock repurchase authorization	$ 500	$ 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