Asset Quality - Allowance for Loan and Lease Losses and Corresponding Loan Balances (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchase Credit Impairment Outstanding	$ 865,000,000	$ 11,000,000
Individually Evaluated for Impairment Allowance, Total ALLL - Including Discontinued Operations	39,000,000	37,000,000
Collectively Evaluated for Impairment Allowance, Total ALLL - Including Discontinued Operations	838,000,000	786,000,000
Purchased Credit Impaired Allowance, Total ALLL - Including Discontinued Operations	5,000,000	1,000,000
Loans Outstanding, Total ALLL - Including Discontinued Operations	87,603,000,000	61,704,000,000
Individually Evaluated for Impairment Outstanding, Total ALLL - Including Discontinued Operations	523,000,000	329,000,000
Collectively Evaluated for Impairment Outstanding, Total ALLL - Including Discontinued Operations	86,215,000,000	61,364,000,000
Purchased Credit Impaired Outstanding, Total ALLL - Including Discontinued Operations	865,000,000	11,000,000
Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	37,000,000	35,000,000
Collectively Evaluated for Impairment Allowance	816,000,000	760,000,000
Purchase Credit Impairment Allowance	5,000,000	1,000,000
Loans Outstanding	86,038,000,000	59,876,000,000
Individually Evaluated for Impairment Outstanding	501,000,000	308,000,000
Collectively Evaluated for Impairment Outstanding	84,672,000,000	59,557,000,000
Purchase Credit Impairment Outstanding	865,000,000	11,000,000
Discontinued Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance		2,000,000
Collectively Evaluated for Impairment Allowance	22,000,000	26,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	1,565,000,000	1,828,000,000
Individually Evaluated for Impairment Outstanding	22,000,000	21,000,000
Collectively Evaluated for Impairment Outstanding	1,543,000,000	1,807,000,000
Purchase Credit Impairment Outstanding	0	0
Loans carried at fair value	3,000,000	4,000,000
Commercial Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Purchase Credit Impairment Allowance	5,000,000	0
Purchase Credit Impairment Outstanding		0
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	17,000,000	7,000,000
Collectively Evaluated for Impairment Allowance	486,000,000	443,000,000
Purchase Credit Impairment Allowance	5,000,000	0
Loans Outstanding	39,768,000,000	31,240,000,000
Individually Evaluated for Impairment Outstanding	284,000,000	68,000,000
Collectively Evaluated for Impairment Outstanding	39,372,000,000	31,172,000,000
Purchase Credit Impairment Outstanding	112,000,000	0
Commercial Loans [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	1,000,000
Collectively Evaluated for Impairment Allowance	144,000,000	133,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	15,111,000,000	7,959,000,000
Individually Evaluated for Impairment Outstanding	5,000,000	10,000,000
Collectively Evaluated for Impairment Outstanding	14,784,000,000	7,949,000,000
Purchase Credit Impairment Outstanding	322,000,000	0
Commercial Loans [Member] | Commercial Real Estate: Construction [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	22,000,000	25,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	2,345,000,000	1,053,000,000
Individually Evaluated for Impairment Outstanding	0	5,000,000
Collectively Evaluated for Impairment Outstanding	2,319,000,000	1,048,000,000
Purchase Credit Impairment Outstanding	26,000,000	0
Commercial Loans [Member] | Commercial Real Estate Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	1,000,000
Collectively Evaluated for Impairment Allowance	166,000,000	158,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	17,456,000,000	9,012,000,000
Individually Evaluated for Impairment Outstanding	5,000,000	15,000,000
Collectively Evaluated for Impairment Outstanding	17,103,000,000	8,997,000,000
Purchase Credit Impairment Outstanding	348,000,000	0
Commercial Loans [Member] | Commercial Lease Financing [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	42,000,000	47,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	4,685,000,000	4,020,000,000
Individually Evaluated for Impairment Outstanding	0	0
Collectively Evaluated for Impairment Outstanding	4,685,000,000	4,020,000,000
Purchase Credit Impairment Outstanding	0	0
Commercial Loans [Member] | Commercial Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	17,000,000	8,000,000
Collectively Evaluated for Impairment Allowance	694,000,000	648,000,000
Loans Outstanding	61,909,000,000	44,272,000,000
Individually Evaluated for Impairment Outstanding	289,000,000	83,000,000
Collectively Evaluated for Impairment Outstanding	61,160,000,000	44,189,000,000
Purchase Credit Impairment Outstanding	460,000,000
Consumer Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans Outstanding		15,604,000,000
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	2,000,000	4,000,000
Collectively Evaluated for Impairment Allowance	15,000,000	13,000,000
Purchase Credit Impairment Allowance	0	1,000,000
Loans Outstanding	5,547,000,000	2,242,000,000
Individually Evaluated for Impairment Outstanding	51,000,000	56,000,000
Collectively Evaluated for Impairment Outstanding	5,128,000,000	2,176,000,000
Purchase Credit Impairment Outstanding	368,000,000	10,000,000
Consumer Loans [Member] | Home Equity Loan [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	17,000,000	20,000,000
Collectively Evaluated for Impairment Allowance	37,000,000	37,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	12,674,000,000	10,335,000,000
Individually Evaluated for Impairment Outstanding	125,000,000	125,000,000
Collectively Evaluated for Impairment Outstanding	12,519,000,000	10,209,000,000
Purchase Credit Impairment Outstanding	30,000,000	1,000,000
Consumer Loans [Member] | Consumer Direct Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	24,000,000	20,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	1,788,000,000	1,600,000,000
Individually Evaluated for Impairment Outstanding	3,000,000	3,000,000
Collectively Evaluated for Impairment Outstanding	1,778,000,000	1,597,000,000
Purchase Credit Impairment Outstanding	7,000,000	0
Consumer Loans [Member] | Consumer Credit Card [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	0	0
Collectively Evaluated for Impairment Allowance	38,000,000	32,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	1,111,000,000	806,000,000
Individually Evaluated for Impairment Outstanding	3,000,000	3,000,000
Collectively Evaluated for Impairment Outstanding	1,108,000,000	803,000,000
Purchase Credit Impairment Outstanding	0	0
Consumer Loans [Member] | Consumer Indirect Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	1,000,000	3,000,000
Collectively Evaluated for Impairment Allowance	8,000,000	10,000,000
Purchase Credit Impairment Allowance	0	0
Loans Outstanding	3,009,000,000	621,000,000
Individually Evaluated for Impairment Outstanding	30,000,000	38,000,000
Collectively Evaluated for Impairment Outstanding	2,979,000,000	583,000,000
Purchase Credit Impairment Outstanding	0	0
Consumer Loans [Member] | Consumer Loans [Member] | Continuing Operations [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually Evaluated for Impairment Allowance	20,000,000	27,000,000
Collectively Evaluated for Impairment Allowance	122,000,000	112,000,000
Purchase Credit Impairment Allowance	0	1,000,000
Loans Outstanding	24,129,000,000
Individually Evaluated for Impairment Outstanding	212,000,000	225,000,000
Collectively Evaluated for Impairment Outstanding	23,512,000,000	15,368,000,000
Purchase Credit Impairment Outstanding	$ 405,000,000	$ 11,000,000