Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Type (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 4,326	$ 4,449	$ 4,375	$ 4,537
Provision for credit losses	282	311	827	941
Loans charged off	372	410	1,135	1,264
Less recoveries of loans charged off	(80)	(74)	(268)	(238)
Net loans charged off	292	336	867	1,026
Other changes	(10)	(10)	(29)	(38)
Balance at end of period	4,306	4,414	4,306	4,414
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,180	1,111	1,146	1,075
Provision for credit losses	114	83	234	210
Loans charged off	91	80	230	219
Less recoveries of loans charged off	(20)	(22)	(74)	(70)
Net loans charged off	71	58	156	149
Other changes			(1)
Balance at end of period	1,223	1,136	1,223	1,136
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	735	725	726	776
Provision for credit losses	(10)	(6)	(18)	(64)
Loans charged off	2	10	16	27
Less recoveries of loans charged off	(13)	(6)	(44)	(30)
Net loans charged off	(11)	4	(28)	(3)
Balance at end of period	736	715	736	715
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	737	848	787	875
Provision for credit losses	(24)	(13)	(6)	74
Loans charged off	31	48	113	171
Less recoveries of loans charged off	(6)	(6)	(20)	(15)
Net loans charged off	25	42	93	156
Balance at end of period	688	793	688	793
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	873	874	880	884
Provision for credit losses	156	162	481	495
Loans charged off	171	174	543	546
Less recoveries of loans charged off	(18)	(16)	(58)	(48)
Net loans charged off	153	158	485	498
Other changes				(3)
Balance at end of period	876	878	876	878
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	752	779	771	781
Provision for credit losses	46	84	134	227
Loans charged off	77	96	233	291
Less recoveries of loans charged off	(23)	(23)	(72)	(73)
Net loans charged off	54	73	161	218
Balance at end of period	744	790	744	790
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	4,277	4,337	4,310	4,391
Provision for credit losses	282	310	825	942
Loans charged off	372	408	1,135	1,254
Less recoveries of loans charged off	(80)	(73)	(268)	(236)
Net loans charged off	292	335	867	1,018
Other changes			(1)	(3)
Balance at end of period	4,267	4,312	4,267	4,312
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	49	112	65	146
Provision for credit losses		1	2	(1)
Loans charged off		2		10
Less recoveries of loans charged off		(1)		(2)
Net loans charged off		1		8
Other changes	(10)	(10)	(28)	(35)
Balance at end of period	$ 39	$ 102	$ 39	$ 102