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Investments - Additional Information (Detail) In Millions, unless otherwise specified | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2012 USD ($) | Dec. 31, 2011 USD ($) | Dec. 31, 2010 USD ($) | Dec. 31, 2012 ABCP [Member] USD ($) | Dec. 31, 2012 ABCP [Member] CAD | Dec. 31, 2011 ABCP [Member] CAD | Jan. 16, 2009 ABCP [Member] CAD
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |
Investments in ABCP |  |  |  |  | 107 | 125 |
Restructuring notes in a Master Trust MAV2-A Notes issued under new restructuring plan |  |  |  |  |  |  | 102
Restructuring notes in a MAV2-B and C Notes issued under new restructuring plan |  |  |  |  |  |  | 9
Tracking notes deemed ineligible for inclusion in the Master Trust |  |  |  |  |  |  | 23
Increase in carrying value of equity method investment |  |  |  | 15 |  |  |
Sales to equity method investees | $ 171 | $ 76 | $ 18 |  |  |  |

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