Loans - Impaired Loans, Excluding Acquired Loans (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Financing Receivable:
With an Allowance	$ 2,052	$ 2,660
Without an Allowance	393	507
Total Recorded Investment	2,445	3,167
Related Allowance	421	465
Net Recorded Investment	2,024	2,702
Unpaid Principal Balance	2,882	3,591
Average Recorded Investment	2,868	2,930	$ 2,138
Interest Income Recognized	155	177	163
Credit Card Portfolio Segment [Member]
Impaired Financing Receivable:
With an Allowance	812	715
Without an Allowance	0	0
Total Recorded Investment	812	715
Related Allowance	292	239
Net Recorded Investment	520	476
Unpaid Principal Balance	792	695
Average Recorded Investment	756	673	674
Interest Income Recognized	74	68	67
Credit Card Portfolio Segment [Member] \| Geographic Distribution, Domestic [Member]
Impaired Financing Receivable:
With an Allowance	639	581
Without an Allowance	0	0
Total Recorded Investment	639	581
Related Allowance	208	174
Net Recorded Investment	431	407
Unpaid Principal Balance	625	566
Average Recorded Investment	602	540	539
Interest Income Recognized	63	58	57
Credit Card Portfolio Segment [Member] \| Geographic Distribution, Foreign [Member]
Impaired Financing Receivable:
With an Allowance	173	134
Without an Allowance	0	0
Total Recorded Investment	173	134
Related Allowance	84	65
Net Recorded Investment	89	69
Unpaid Principal Balance	167	129
Average Recorded Investment	154	133	135
Interest Income Recognized	11	10	10
Consumer Portfolio Segment [Member]
Impaired Financing Receivable:
With an Allowance	606	609
Without an Allowance	169	334
Total Recorded Investment	775	943
Related Allowance	53	57
Net Recorded Investment	722	886
Unpaid Principal Balance	1,094	1,336
Average Recorded Investment	853	924	882
Interest Income Recognized	59	93	88
Consumer Portfolio Segment [Member] \| Auto
Impaired Financing Receivable:
With an Allowance	363	316
Without an Allowance	118	207
Total Recorded Investment	481	523
Related Allowance	30	24
Net Recorded Investment	451	499
Unpaid Principal Balance	730	807
Average Recorded Investment	495	501	462
Interest Income Recognized	53	86	82
Consumer Portfolio Segment [Member] \| Home loan
Impaired Financing Receivable:
With an Allowance	192	241
Without an Allowance	41	117
Total Recorded Investment	233	358
Related Allowance	15	19
Net Recorded Investment	218	339
Unpaid Principal Balance	298	464
Average Recorded Investment	299	361	364
Interest Income Recognized	5	5	4
Consumer Portfolio Segment [Member] \| Retail banking
Impaired Financing Receivable:
With an Allowance	51	52
Without an Allowance	10	10
Total Recorded Investment	61	62
Related Allowance	8	14
Net Recorded Investment	53	48
Unpaid Principal Balance	66	65
Average Recorded Investment	59	62	56
Interest Income Recognized	1	2	2
Commercial Banking
Impaired Financing Receivable:
With an Allowance	634	1,336
Without an Allowance	224	173
Total Recorded Investment	858	1,509
Related Allowance	76	169
Net Recorded Investment	782	1,340
Unpaid Principal Balance	996	1,560
Average Recorded Investment	1,259	1,333	582
Interest Income Recognized	22	16	8
Commercial Banking \| Total commercial lending
Impaired Financing Receivable:
With an Allowance	627	1,332
Without an Allowance	224	173
Total Recorded Investment	851	1,505
Related Allowance	76	169
Net Recorded Investment	775	1,336
Unpaid Principal Balance	987	1,556
Average Recorded Investment	1,252	1,326	575
Interest Income Recognized	22	16	8
Commercial Banking \| Commercial and multifamily real estate
Impaired Financing Receivable:
With an Allowance	138	83
Without an Allowance	2	29
Total Recorded Investment	140	112
Related Allowance	13	7
Net Recorded Investment	127	105
Unpaid Principal Balance	143	112
Average Recorded Investment	134	111	109
Interest Income Recognized	4	3	3
Commercial Banking \| Commercial and industrial
Impaired Financing Receivable:
With an Allowance	489	1,249
Without an Allowance	222	144
Total Recorded Investment	711	1,393
Related Allowance	63	162
Net Recorded Investment	648	1,231
Unpaid Principal Balance	844	1,444
Average Recorded Investment	1,118	1,215	466
Interest Income Recognized	18	13	5
Commercial Banking \| Small-ticket commercial real estate
Impaired Financing Receivable:
With an Allowance	7	4
Without an Allowance	0	0
Total Recorded Investment	7	4
Related Allowance	0	0
Net Recorded Investment	7	4
Unpaid Principal Balance	9	4
Average Recorded Investment	7	7	7
Interest Income Recognized	$ 0	$ 0	$ 0

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953550-111524

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