Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 292,028	$ 286,810
Total outstanding commitments	617,808	606,656
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	288,045	282,228
Total outstanding commitments	612,606	600,407
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,513	1,740
Total outstanding commitments	2,136	2,801
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,470	2,842
Total outstanding commitments	3,066	3,448
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,983	4,582
Total outstanding commitments	5,202	6,249
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	103,980	102,444
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	101,842	100,014
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,082	1,149
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,056	1,281
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,138	2,430
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,334	39,539
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	38,481	38,473
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	425	584
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	428	482
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	853	1,066
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	67,913	65,034
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	67,485	64,570
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	1
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	425	463
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	428	464
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	57,375	56,430
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	57,078	56,101
Other Retail [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	6
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	294	323
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	297	329
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23,426	23,363
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23,159	23,070
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	267	293
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 267	$ 293