Asset Quality - Financing Receivable Credit Quality Indicators (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 53,101	$ 52,822	$ 49,605
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	23,715	23,242	20,916
Commercial, Financial and Agricultural [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	275		165
Commercial, Financial and Agricultural [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	618		680
Commercial, Financial and Agricultural [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	21,355		18,182
Commercial, Financial and Agricultural [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	560		868
Commercial, Financial and Agricultural [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	907		1,021
Commercial, Financial and Agricultural [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	23,715		20,916
RE Commercial [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1
RE Commercial [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	74		64
RE Commercial [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	6,600		5,925
RE Commercial [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	364		553
RE Commercial [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	433		867
RE Commercial [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	7,472		7,409
RE Construction [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1		1
RE Construction [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1		1
RE Construction [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	871		791
RE Construction [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	23		58
RE Construction [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	164		321
RE Construction [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,060		1,172
Commercial Lease Financing [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	485		605
Commercial Lease Financing [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,011		992
Commercial Lease Financing [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,046		3,179
Commercial Lease Financing [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	145		197
Commercial Lease Financing [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	87		133
Commercial Lease Financing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,774		5,106
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	37,023	36,880	34,603
Commercial Loans [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	762		771
Commercial Loans [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,704		1,737
Commercial Loans [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	31,872		28,077
Commercial Loans [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,092		1,676
Commercial Loans [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,591		2,342
Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 37,021		$ 34,603