|
Profit sharing plans (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2011
|
Dec. 31, 2010
|
Dec. 31, 2009
|
|
| Profit sharing plans [Abstract] | |||
| Minimum percentage amount of operating margin the company must attain for full calendar year for any profit sharing per individual to be paid (in hundredths) | 10.00% | ||
| Maximum amount of gross compensation eligible for profit sharing deferral per individual in calendar year when minimum operating margin is attained by company (in hundredths) | 2.00% | ||
| Maximum amount of gross compensation eligible for profit sharing per individual in calendar year when 35% operating margin is attained by company (in hundredths) | 20.00% | ||
| Percentage of operating margin the company must attain for full calendar year for maximum amount of profit sharing per individual to be paid (in hundredths) | 35.00% | ||
| Profit sharing expense per period under profit sharing plan | $ 143 | $ 279 | $ 102 |