Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 287,699	$ 286,810
Total outstanding commitments	613,082	606,656
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	283,400	282,228
Total outstanding commitments	607,486	600,407
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,507	1,740
Total outstanding commitments	2,191	2,801
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,792	2,842
Total outstanding commitments	3,405	3,448
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,299	4,582
Total outstanding commitments	5,596	6,249
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	103,069	102,444
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	100,888	100,014
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	969	1,149
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,212	1,281
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,181	2,430
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,421	39,539
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	38,368	38,473
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	532	584
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	521	482
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,053	1,066
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	66,243	65,034
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	65,779	64,570
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		1
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	464	463
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	464	464
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	56,698	56,430
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	56,385	56,101
Other Retail [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	6
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	307	323
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	313	329
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,268	23,363
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,980	23,070
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	288	293
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 288	$ 293