|
Stockholders' equity (Details Textual) (USD $)
In Billions, except Per Share data, unless otherwise specified |
1 Months Ended | 3 Months Ended | |||
|---|---|---|---|---|---|
|
Mar. 07, 2013
|
Mar. 06, 2013
|
Dec. 13, 2012
|
Mar. 31, 2013
|
Mar. 31, 2012
|
|
| Equity [Abstract] | |||||
| Amount available for stock repurchases under a board approved stock repurchase plan | $ 1.6 | ||||
| Common stock, dividends declared per share (in usd per share) | $ 0.47 | $ 0.47 | |||
| Dividends paid per share (in usd per share) | $ 0.47 | $ 0.47000000 | $ 0.36000000 | ||