|
Stockholders' equity (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|
|
Sep. 30, 2012
|
Jun. 30, 2012
|
Mar. 31, 2012
|
Sep. 30, 2011
|
Jun. 30, 2011
|
Mar. 31, 2011
|
Sep. 30, 2012
|
Sep. 30, 2011
|
|
| Stock repurchase program | ||||||||
| Stock repurchases, in shares | 9.7 | 17.4 | 21.0 | 45.4 | 12.9 | 0 | 48.1 | 58.3 |
| Stock repurchases, in dollars | $ 797 | $ 1,203 | $ 1,429 | $ 2,421 | $ 732 | $ 0 | $ 3,429 | $ 3,153 |