Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 4,417	$ 4,357
Provision for credit losses	341	345
Loans charged-off	453	417
Less recoveries of loans charged-off	(112)	(82)
Net loans charged-off	341	335
Other changes		(1)
Balance at end of period	4,417	4,366
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,372	1,450
Provision for credit losses	74	54
Loans charged-off	94	96
Less recoveries of loans charged-off	(34)	(21)
Net loans charged-off	60	75
Balance at end of period	1,386	1,429
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	831	812
Provision for credit losses	(8)	28
Loans charged-off	3	3
Less recoveries of loans charged-off	(6)	(5)
Net loans charged-off	(3)	(2)
Balance at end of period	826	842
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	449	510
Provision for credit losses	1	(13)
Loans charged-off	13	17
Less recoveries of loans charged-off	(6)	(5)
Net loans charged-off	7	12
Balance at end of period	443	485
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	678	617
Provision for credit losses	60	65
Loans charged-off	95	89
Less recoveries of loans charged-off	(29)	(29)
Net loans charged-off	66	60
Balance at end of period	672	622
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,056	934
Provision for credit losses	219	211
Loans charged-off	248	212
Less recoveries of loans charged-off	(37)	(22)
Net loans charged-off	211	190
Balance at end of period	1,064	955
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	4,386	4,323
Provision for credit losses	346	345
Loans charged-off	453	417
Less recoveries of loans charged-off	(112)	(82)
Net loans charged-off	341	335
Balance at end of period	4,391	4,333
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	31	34
Provision for credit losses	(5)
Other changes		(1)
Balance at end of period	$ 26	$ 33