Acquisitions and Discontinued Operations - Combined Results of Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income taxes	$ 3	$ 2
Income (loss) from discontinued operations, net of taxes	5	4
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	10	24
Provision for credit losses	2	4
Net interest income after provision for credit losses	8	20
Noninterest income	4	(4)
Noninterest expense	4	10
Income (loss) before income taxes	8	6
Income taxes	3	2
Income (loss) from discontinued operations, net of taxes	$ 5	$ 4

Discontinued Operation Noninterest Expense

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Discontinued Operation Noninterest Income

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Discontinued Operation Provision For Losses

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Disposal Group Including Discontinued Operation Interest Income Expense Net

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Overall income (loss) from a disposal group that is classified as a component of the entity, before income tax, reported as a separate component of income before extraordinary items. Includes the following (before income tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Tax effect allocated to a disposal group that is classified as a component of the entity reported as a separate component of income before extraordinary items. Includes the tax effects of the following: income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Amount of interest income attributable to disposal group.

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Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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