Asset Quality - Financing Receivable Credit Quality Indicators (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 57,381	$ 54,457
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	27,982	24,963
Commercial, Financial and Agricultural [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	311	402
Commercial, Financial and Agricultural [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,272	882
Commercial, Financial and Agricultural [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	24,949	22,368
Commercial, Financial and Agricultural [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	686	521
Commercial, Financial and Agricultural [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	764	790
RE Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	8,047	7,719
RE Commercial [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2	2
RE Commercial [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1	56
RE Commercial [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	7,527	7,129
RE Commercial [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	287	282
RE Commercial [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	230	250
Commercial Real Estate Construction Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,100	1,093
Commercial Real Estate Construction Financing Receivable [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1	1
Commercial Real Estate Construction Financing Receivable [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans		1
Commercial Real Estate Construction Financing Receivable [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	956	920
Commercial Real Estate Construction Financing Receivable [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	105	32
Commercial Real Estate Construction Financing Receivable [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	38	139
Commercial Leases
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,252	4,551
Commercial Leases | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	513	656
Commercial Leases | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	608	631
Commercial Leases | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,952	3,080
Commercial Leases | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	112	117
Commercial Leases | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	67	67
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	41,381	38,327
Commercial Loans [Member] | AAA-AA [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	827	1,061
Commercial Loans [Member] | A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,881	1,570
Commercial Loans [Member] | BBB-BB [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	36,384	33,497
Commercial Loans [Member] | B [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,190	952
Commercial Loans [Member] | CCC-C [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,099	$ 1,246