Asset Quality - Financing Receivable Credit Quality Indicators (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 86,492	$ 86,038	$ 85,528
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41,054	39,656
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,171	37,845
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,714	1,514
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	169	297
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,654	14,789
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,188	14,308
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	436	455
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	30	26
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,930	2,319
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,893	2,287
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	35	30
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	2
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,716	4,685
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,615	4,632
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	91	45
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10	8
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Portfolio Segment Excluding PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	62,354	61,449
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Portfolio Segment Excluding PCI Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	59,867	59,072
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,276	2,044
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	211	333
Commercial Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	392	460
Commercial Portfolio Segment, PCI [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	218	172
Commercial Portfolio Segment, PCI [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	174	288
Commercial Portfolio Segment, PCI [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	93	112
Commercial Portfolio Segment, PCI [Member] | Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	40	12
Commercial Portfolio Segment, PCI [Member] | Commercial and Industrial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	53	100
Commercial Portfolio Segment, PCI [Member] | RE Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	275	322
Commercial Portfolio Segment, PCI [Member] | RE Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	154	139
Commercial Portfolio Segment, PCI [Member] | RE Commercial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	121	183
Commercial Portfolio Segment, PCI [Member] | RE Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	24	26
Commercial Portfolio Segment, PCI [Member] | RE Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	24	21
Commercial Portfolio Segment, PCI [Member] | RE Construction [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	5
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0