Loans - TDR Disclosures in Progress Financial Impact of Modification (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Modifications [Line Items]
Total Loans Modified	$ 356	$ 442	$ 731	$ 714
Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Total Loans Modified	126	95	267	193
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Total Loans Modified	71	93	156	195
Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Modifications [Line Items]
Total Loans Modified	61	77	136	163
Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Modifications [Line Items]
Total Loans Modified	6	12	14	25
Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Modifications [Line Items]
Total Loans Modified	4	4	6	7
Commercial Banking
Financing Receivable, Modifications [Line Items]
Total Loans Modified	159	254	308	326
Commercial Banking | Total commercial lending
Financing Receivable, Modifications [Line Items]
Total Loans Modified	158	254	307	326
Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Modifications [Line Items]
Total Loans Modified	24	0	26	25
Commercial Banking | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Total Loans Modified	134	254	281	301
Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Modifications [Line Items]
Total Loans Modified	$ 1	$ 0	$ 1	$ 0
Reduced Interest Rate
Financing Receivable, Modifications [Line Items]
% of TDR Activity	52.00%	38.00%	51.00%	43.00%
Average Rate Reduction	13.35%	10.82%	13.68%	11.93%
Reduced Interest Rate | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	100.00%	100.00%	100.00%	100.00%
Average Rate Reduction	18.12%	17.47%	17.92%	17.50%
Reduced Interest Rate | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	49.00%	47.00%	51.00%	45.00%
Average Rate Reduction	3.54%	3.64%	3.66%	3.69%
Reduced Interest Rate | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Modifications [Line Items]
% of TDR Activity	52.00%	46.00%	52.00%	44.00%
Average Rate Reduction	3.65%	3.86%	3.85%	3.89%
Reduced Interest Rate | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Modifications [Line Items]
% of TDR Activity	47.00%	52.00%	54.00%	57.00%
Average Rate Reduction	3.14%	2.29%	2.49%	2.47%
Reduced Interest Rate | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Modifications [Line Items]
% of TDR Activity	18.00%	47.00%	30.00%	36.00%
Average Rate Reduction	0.10%	4.10%	1.19%	5.02%
Reduced Interest Rate | Commercial Banking
Financing Receivable, Modifications [Line Items]
% of TDR Activity	15.00%	12.00%	9.00%	9.00%
Average Rate Reduction	2.23%	0.00%	1.13%	0.05%
Reduced Interest Rate | Commercial Banking | Total commercial lending
Financing Receivable, Modifications [Line Items]
% of TDR Activity	15.00%	12.00%	9.00%	9.00%
Average Rate Reduction	2.23%	0.00%	1.13%	0.05%
Reduced Interest Rate | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	8.00%	0.00%
Average Rate Reduction	0.00%	0.00%	0.02%	0.00%
Reduced Interest Rate | Commercial Banking | Commercial and industrial
Financing Receivable, Modifications [Line Items]
% of TDR Activity	18.00%	12.00%	9.00%	10.00%
Average Rate Reduction	2.23%	0.06%	1.23%	0.05%
Reduced Interest Rate | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Rate Reduction	0.00%	0.00%	0.00%	0.00%
Term Extension
Financing Receivable, Modifications [Line Items]
% of TDR Activity	37.00%	53.00%	32.00%	49.00%
Average Term Extension (Months)	17 months	32 months	22 months	30 months
Term Extension | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Term Extension (Months)	0 months	0 months	0 months	0 months
Term Extension | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	96.00%	77.00%	91.00%	75.00%
Average Term Extension (Months)	25 months	46 months	25 months	43 months
Term Extension | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Modifications [Line Items]
% of TDR Activity	99.00%	75.00%	93.00%	74.00%
Average Term Extension (Months)	7 months	7 months	7 months	7 months
Term Extension | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Modifications [Line Items]
% of TDR Activity	87.00%	95.00%	83.00%	85.00%
Average Term Extension (Months)	233 months	252 months	227 months	250 months
Term Extension | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Modifications [Line Items]
% of TDR Activity	59.00%	58.00%	62.00%	70.00%
Average Term Extension (Months)	13 months	10 months	11 months	10 months
Term Extension | Commercial Banking
Financing Receivable, Modifications [Line Items]
% of TDR Activity	41.00%	64.00%	31.00%	61.00%
Average Term Extension (Months)	9 months	25 months	17 months	21 months
Term Extension | Commercial Banking | Total commercial lending
Financing Receivable, Modifications [Line Items]
% of TDR Activity	41.00%	64.00%	31.00%	62.00%
Average Term Extension (Months)	9 months	25 months	17 months	21 months
Term Extension | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Modifications [Line Items]
% of TDR Activity	10.00%	0.00%	17.00%	100.00%
Average Term Extension (Months)	4 months	0 months	5 months	8 months
Term Extension | Commercial Banking | Commercial and industrial
Financing Receivable, Modifications [Line Items]
% of TDR Activity	47.00%	64.00%	32.00%	58.00%
Average Term Extension (Months)	9 months	25 months	18 months	23 months
Term Extension | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Term Extension (Months)	0 months	0 months	0 months	0 months
Balance Reduction
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	5.00%	0.00%	6.00%
Gross Balance Reduction	$ 0	$ 16	$ 7	$ 37
Balance Reduction | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	22.00%	5.00%	22.00%
Gross Balance Reduction	$ 0	$ 16	$ 7	$ 37
Balance Reduction | Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	25.00%	6.00%	26.00%
Gross Balance Reduction	$ 0	$ 15	$ 7	$ 36
Balance Reduction | Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Modifications [Line Items]
% of TDR Activity	5.00%	2.00%	2.00%	2.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	35.00%	0.00%	20.00%
Gross Balance Reduction	$ 0	$ 1	$ 0	$ 1
Balance Reduction | Commercial Banking
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Total commercial lending
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Commercial and multifamily real estate
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Commercial and industrial
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Balance Reduction | Commercial Banking | Small-ticket commercial real estate
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Geographic Distribution, Domestic [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Total Loans Modified	$ 87	$ 62	$ 184	$ 124
Geographic Distribution, Domestic [Member] | Reduced Interest Rate | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	100.00%	100.00%	100.00%	100.00%
Average Rate Reduction	14.36%	12.81%	14.09%	12.83%
Geographic Distribution, Domestic [Member] | Term Extension | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Term Extension (Months)	0 months	0 months	0 months	0 months
Geographic Distribution, Domestic [Member] | Balance Reduction | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0
Geographic Distribution, Foreign [Member] | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Total Loans Modified	$ 39	$ 33	$ 83	$ 69
Geographic Distribution, Foreign [Member] | Reduced Interest Rate | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	100.00%	100.00%	100.00%	100.00%
Average Rate Reduction	26.50%	26.01%	26.33%	25.83%
Geographic Distribution, Foreign [Member] | Term Extension | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Average Term Extension (Months)	0 months	0 months	0 months	0 months
Geographic Distribution, Foreign [Member] | Balance Reduction | Credit Card Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
% of TDR Activity	0.00%	0.00%	0.00%	0.00%
Gross Balance Reduction	$ 0	$ 0	$ 0	$ 0