Acquisitions and Discontinued Operations - Components of Income (Loss) from Discontinued Operations, Net of Taxes (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
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 Operations [Member] \| Austin Capital Management [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Noninterest expense		4
Income (loss) before income taxes		(4)
Income taxes		(2)
Income (loss) from discontinued operations, net of taxes		(2)
Discontinued Operations [Member] \| Victory Capital Management [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income		1
Noninterest income		10
Income (loss) before income taxes		11
Income taxes		4
Income (loss) from discontinued operations, net of taxes		$ 7

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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- Definition

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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