Loans and Allowance for Credit Losses - Additional Detail of Allowance for Credit Losses and Related Loan Balances by Portfolio Type (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Allowance Balance at End of Period
Loans individually evaluated for impairment	$ 46	$ 13
TDRs collectively evaluated for impairment	318	345
Other loans collectively evaluated for impairment	3,910	3,900
Loans acquired with deteriorated credit quality	46	48
Total allowance for credit losses	4,320	4,306	$ 4,351	$ 4,375
Loan Balance at End of Period
Loans individually evaluated for impairment	657	390
TDRs collectively evaluated for impairment	4,919	5,070
Other loans collectively evaluated for impairment	256,201	252,590
Loans acquired with deteriorated credit quality	2,745	2,799
Total loans	260,093	256,253
Total loans	264,522	260,849
Commercial [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	45	11
TDRs collectively evaluated for impairment	6	10
Other loans collectively evaluated for impairment	1,390	1,266
Total allowance for credit losses	1,441	1,287	1,200	1,146
Loan Balance at End of Period
Loans individually evaluated for impairment	616	336
TDRs collectively evaluated for impairment	155	138
Other loans collectively evaluated for impairment	90,505	87,927
Loans acquired with deteriorated credit quality	1	1
Total loans	91,277	88,402
Commercial Real Estate [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	1	2
TDRs collectively evaluated for impairment	1	7
Other loans collectively evaluated for impairment	720	703
Loans acquired with deteriorated credit quality	12	12
Total allowance for credit losses	734	724	721	726
Loan Balance at End of Period
Loans individually evaluated for impairment	28	41
TDRs collectively evaluated for impairment	220	235
Other loans collectively evaluated for impairment	42,205	41,566
Loans acquired with deteriorated credit quality	290	295
Total loans	42,743	42,137
Residential Mortgages [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	221	236
Other loans collectively evaluated for impairment	335	395
Total allowance for credit losses	556	631	764	787
Loan Balance at End of Period
Loans individually evaluated for impairment	13	13
TDRs collectively evaluated for impairment	4,093	4,241
Other loans collectively evaluated for impairment	50,848	49,241
Loans acquired with deteriorated credit quality	1	1
Total loans	54,955	53,496
Other Retail [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	32	33
Other loans collectively evaluated for impairment	646	710
Total allowance for credit losses	678	743	738	771
Loan Balance at End of Period
TDRs collectively evaluated for impairment	204	211
Other loans collectively evaluated for impairment	50,957	50,995
Total loans	51,161	51,206
Credit Card [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	57	57
Other loans collectively evaluated for impairment	818	826
Total allowance for credit losses	875	883	871	880
Loan Balance at End of Period
TDRs collectively evaluated for impairment	212	210
Other loans collectively evaluated for impairment	19,745	20,802
Total loans	19,957	21,012
Total Loans, Excluding Covered Loans [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	46	13
TDRs collectively evaluated for impairment	317	343
Other loans collectively evaluated for impairment	3,909	3,900
Loans acquired with deteriorated credit quality	12	12
Total allowance for credit losses	4,284	4,268	4,294	4,310
Loan Balance at End of Period
Loans individually evaluated for impairment	657	390
TDRs collectively evaluated for impairment	4,884	5,035
Other loans collectively evaluated for impairment	254,260	250,531
Loans acquired with deteriorated credit quality	292	297
Total loans	260,093	256,253
Covered Loans [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	1	2
Other loans collectively evaluated for impairment	1
Loans acquired with deteriorated credit quality	34	36
Total allowance for credit losses	36	38	$ 57	$ 65
Loan Balance at End of Period
TDRs collectively evaluated for impairment	35	35
Other loans collectively evaluated for impairment	1,941	2,059
Loans acquired with deteriorated credit quality	2,453	2,502
Total loans	$ 4,429	$ 4,596