Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 4,417	$ 4,366	$ 4,417	$ 4,357
Provision for credit losses	327	350	668	695
Loans charged-off	437	437	890	854
Less recoveries of loans charged-off	(105)	(97)	(217)	(179)
Net loans charged-off	332	340	673	675
Other changes	(1)	1	(1)
Balance at end of period	4,411	4,377	4,411	4,377
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,386	1,429	1,372	1,450
Provision for credit losses	63	44	137	98
Loans charged-off	83	104	177	200
Less recoveries of loans charged-off	(25)	(26)	(59)	(47)
Net loans charged-off	58	78	118	153
Balance at end of period	1,391	1,395	1,391	1,395
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	826	842	831	812
Provision for credit losses	(14)	5	(22)	33
Loans charged-off	2	2	5	5
Less recoveries of loans charged-off	(2)	(11)	(8)	(16)
Net loans charged-off		(9)	(3)	(11)
Balance at end of period	812	856	812	856
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	443	485	449	510
Provision for credit losses	(3)	(22)	(2)	(35)
Loans charged-off	12	16	25	33
Less recoveries of loans charged-off	(8)	(8)	(14)	(13)
Net loans charged-off	4	8	11	20
Balance at end of period	436	455	436	455
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	672	622	678	617
Provision for credit losses	55	85	115	150
Loans charged-off	92	88	187	177
Less recoveries of loans charged-off	(32)	(29)	(61)	(58)
Net loans charged-off	60	59	126	119
Balance at end of period	667	648	667	648
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,064	955	1,056	934
Provision for credit losses	228	239	447	450
Loans charged-off	248	227	496	439
Less recoveries of loans charged-off	(38)	(23)	(75)	(45)
Net loans charged-off	210	204	421	394
Balance at end of period	1,082	990	1,082	990
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	4,391	4,333	4,386	4,323
Provision for credit losses	329	351	675	696
Loans charged-off	437	437	890	854
Less recoveries of loans charged-off	(105)	(97)	(217)	(179)
Net loans charged-off	332	340	673	675
Balance at end of period	4,388	4,344	4,388	4,344
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	26	33	31	34
Provision for credit losses	(2)	(1)	(7)	(1)
Other changes	(1)	1	(1)
Balance at end of period	$ 23	$ 33	$ 23	$ 33