Loans and Loans Held for Sale - Loans by Category (Parenthetical) (Detail) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, financial and agricultural	$ 28,783,000,000	$ 26,224,000,000	$ 27,982,000,000
Commercial lease financing includes receivables held as collateral for secured borrowing	230,000,000	124,000,000	302,000,000
Purchased loans	130,000,000	159,000,000	138,000,000
Education Lending [Member] \| Discontinued Operations [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,200,000,000	4,400,000,000	2,300,000,000
Commercial Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial, financial and agricultural	87,000,000	95,000,000	88,000,000
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased loans	$ 12,000,000	$ 16,000,000	$ 13,000,000

Reflects the aggregate carrying amount of all categories of loans and leases held in portfolio.

No definition available.

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- Definition

Reflects the aggregate value of loans, trade receivables, securities and financial instruments that serve as collateral for obligations arising from a transfer of financial assets recorded as a secured borrowing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5086-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=34720971&loc=SL6224234-111729

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- Definition

Amount before allowance of loans issued to agricultural, commercial and industrial, and financial institutions. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5066-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(a)(1))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph a(1)

-Article 9

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- Definition

The cash outflow associated with purchasing loans held for investment purposes during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585

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