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Debt And Commitments - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Period of revolving credit facility | 4 years |  |
Borrowings under revolving credit facility | $ 2,250,000,000 |  |
Line of credit facility borrowing capacity, replaced | 2,000,000,000 |  |
Line of credit facility fully transferable amount | 100,000,000 |  |
Interest paid in cash | $ 32,000,000 | $ 19,000,000 | $ 11,000,000

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