Subsequent event (Details) (Common Stock, USD $)	0 Months Ended
Mar. 19, 2013	Dec. 04, 2013 Subsequent event
Subsequent event
Common stock repurchase program, increase in the authorized amount	$ 500,000,000	$ 1,000,000,000
Remaining authorization available under the common stock repurchase program		$ 1,220,000,000

Amount remaining of a stock repurchase plan authorized by an entity's Board of Directors.

No definition available.

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