|
Stock-based compensation (National Acquisition-Related Equity Awards) (Details) (USD $)
In Millions, unless otherwise specified |
Dec. 31, 2011
|
Sep. 23, 2011
|
|---|---|---|
| Business Combinations [Abstract] | ||
| Future compensation cost not yet recognized in the statements of income | $ 477 | |
|
National [Member]
|
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| Business Combinations [Abstract] | ||
| Acquisition-related equity awards, Total estimated fair value | 147 | |
| Acquisition-related equity awards, Pre-combination vested service provided by employees, included in the total consideration transferred | 22 | |
| Acquisition-related equity awards, Post-combination stock-based compensation expense recognized as employees provide service over the remaining vesting periods | 125 | |
| Future compensation cost not yet recognized in the statements of income | $ 68 |