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Additional Financial Information - Additional Information (Detail) (USD $)
In Billions, except Share data in Millions, unless otherwise specified |
12 Months Ended |
|---|---|
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Dec. 31, 2012
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| Supplemental Cash Flow Information [Line Items] | |
| Common shares issued from treasury related to dividend payments | 24.6 |
| Aggregate value of common shares issued from treasury related to dividend payments | $ 1.0 |