Subsequent event (Details) (Subsequent event, Common Stock, USD $)	0 Months Ended
	Mar. 10, 2015	Mar. 10, 2015
Subsequent event | Common Stock
Subsequent event
Common stock repurchase program, increase in the authorized amount	$ 1,000,000,000
Remaining authorization available under the common stock repurchase program	$ 1,200,000,000	$ 1,200,000,000
Approved quarterly cash dividend	$ 0.22	$ 0.22