Variable Interest Entities (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Variable Interest Entity [Line Items]
Carrying amounts of assets	$ 22,132	$ 26,873	$ 29,370
Carrying amounts of liabilities	19,545	25,150
Net realized gains or losses related to deconsolidation	0
Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Carrying amounts of assets	8,200	10,900
Carrying amounts of liabilities	$ 7,200	$ 9,900

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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The amount of the gain (loss) recognized by the parent and included in its attributable portion of net income for the period due to deconsolidation of a subsidiary or derecognition of a group of assets. The gain (loss) recognized and included in the net income attributable to the parent for the period is generally computed as the difference between: (a) the aggregate of: (1) the fair value of any consideration received; (2) the fair value of any retained noncontrolling investment in the former subsidiary at the date the subsidiary was deconsolidated; and (3) the carrying amount of any noncontrolling interest in the former subsidiary (including any accumulated other comprehensive income attributable to the noncontrolling interest) at the date the subsidiary was deconsolidated and (b) the carrying amount of the former subsidiary's assets and liabilities.

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