Loans - Consumer Banking: Risk Profile by Geographic Region, Delinquency Status and Performing Status (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 213,329	$ 208,316	$ 201,592
Past due	6,294	6,070
Nonperforming Loans	$ 1,063	$ 809
Financing Receivable, Nonaccrual, Percent Past Due	0.50%	0.39%
30 Plus day delinquencies (as percent)	2.95%	2.91%
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 70,990	$ 71,439
Percentage of portfolio	100.00%	100.00%
Past due	$ 2,995	$ 3,024
Nonperforming Loans	$ 538	$ 549
Financing Receivable, Nonaccrual, Percent Past Due	0.76%	0.77%
30 Plus day delinquencies (as percent)	4.22%	4.23%
30 plus day delinquencies, excluding acquired loans (as percent)	5.83%	6.28%
90 plus day delinquencies, excluding acquired loans (as percent)	0.77%	0.89%
Nonperforming loans, excluding acquired loans (as percent)	1.05%	1.14%
Consumer Portfolio Segment [Member] | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 41,052	$ 37,824
Past due	2,704	2,682
Nonperforming Loans	$ 201	$ 197
Financing Receivable, Nonaccrual, Percent Past Due	0.49%	0.52%
30 Plus day delinquencies (as percent)	6.59%	7.09%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 41,052	$ 37,824
Percentage of portfolio	57.80%	53.00%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 5,449	$ 5,248
Percentage of portfolio	7.70%	7.40%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 4,502	$ 4,081
Percentage of portfolio	6.30%	5.70%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,889	$ 1,773
Percentage of portfolio	2.70%	2.50%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,839	$ 1,676
Percentage of portfolio	2.60%	2.40%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 3,216	$ 2,737
Percentage of portfolio	4.50%	3.80%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | Georgia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 2,230	$ 2,066
Percentage of portfolio	3.10%	2.90%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,711	$ 1,566
Percentage of portfolio	2.40%	2.20%
Consumer Portfolio Segment [Member] | Auto | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 20,216	$ 18,677
Percentage of portfolio	28.50%	26.10%
Consumer Portfolio Segment [Member] | Home loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 26,340	$ 30,035
Past due	248	302
Nonperforming Loans	$ 310	$ 330
Financing Receivable, Nonaccrual, Percent Past Due	1.18%	1.10%
30 Plus day delinquencies (as percent)	0.94%	1.01%
30 plus day delinquencies, excluding acquired loans (as percent)	3.66%	4.45%
90 plus day delinquencies, excluding acquired loans (as percent)	2.62%	3.21%
Nonperforming loans, excluding acquired loans (as percent)	4.59%	4.86%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 26,340	$ 30,035
Percentage of portfolio	37.10%	42.00%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 6,044	$ 6,943
Percentage of portfolio	8.50%	9.70%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 2,243	$ 2,452
Percentage of portfolio	3.20%	3.40%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,598	$ 1,873
Percentage of portfolio	2.30%	2.60%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | Maryland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,580	$ 1,720
Percentage of portfolio	2.20%	2.40%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,367	$ 1,529
Percentage of portfolio	1.90%	2.10%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | Virginia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,403	$ 1,538
Percentage of portfolio	2.00%	2.20%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,213	$ 1,375
Percentage of portfolio	1.70%	1.90%
Consumer Portfolio Segment [Member] | Home loan | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 10,892	$ 12,605
Percentage of portfolio	15.30%	17.70%
Consumer Portfolio Segment [Member] | Retail banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 3,598	$ 3,580
Past due	43	40
Nonperforming Loans	$ 27	$ 22
Financing Receivable, Nonaccrual, Percent Past Due	0.74%	0.61%
30 Plus day delinquencies (as percent)	1.20%	1.11%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 3,598	$ 3,580
Percentage of portfolio	5.10%	5.00%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 763	$ 756
Percentage of portfolio	1.10%	1.10%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,097	$ 1,120
Percentage of portfolio	1.50%	1.50%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 901	$ 881
Percentage of portfolio	1.30%	1.20%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable | Maryland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 175	$ 167
Percentage of portfolio	0.20%	0.20%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 250	$ 265
Percentage of portfolio	0.40%	0.40%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable | Virginia
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 146	$ 132
Percentage of portfolio	0.20%	0.20%
Consumer Portfolio Segment [Member] | Retail banking | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 266	$ 259
Percentage of portfolio	0.40%	0.40%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past due	$ 1,849	$ 1,805
30 Plus day delinquencies (as percent)	0.87%	0.87%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past due	$ 397	$ 431
30 Plus day delinquencies (as percent)	0.56%	0.60%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past due	$ 201	$ 197
30 Plus day delinquencies (as percent)	0.49%	0.52%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Home loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past due	$ 178	$ 218
30 Plus day delinquencies (as percent)	0.67%	0.73%
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member] | Retail banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past due	$ 18	$ 16
30 Plus day delinquencies (as percent)	0.51%	0.44%