Loans - Commercial Banking: Risk Profile by Geographic Region and Internal Risk Rating (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
Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 52,112	$ 50,890
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 21,855	$ 21,997
Percentage of portfolio	41.90%	43.20%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | Mid-Atlantic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 5,014	$ 4,642
Percentage of portfolio	9.60%	9.10%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 15,251	$ 15,428
Percentage of portfolio	29.30%	30.30%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 9,992	$ 8,823
Percentage of portfolio	19.20%	17.40%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 49,934	$ 49,284
Percentage of portfolio	95.80%	96.90%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,725	$ 1,431
Percentage of portfolio	3.30%	2.80%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 453	$ 175
Percentage of portfolio	0.90%	0.30%
Commercial Banking | Commercial and multifamily real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 23,585	$ 23,137
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Commercial and multifamily real estate | Geographic Concentration Risk | Loans Receivable | Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 14,670	$ 15,135
Percentage of portfolio	62.20%	65.40%
Commercial Banking | Commercial and multifamily real estate | Geographic Concentration Risk | Loans Receivable | Mid-Atlantic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 2,743	$ 2,491
Percentage of portfolio	11.60%	10.80%
Commercial Banking | Commercial and multifamily real estate | Geographic Concentration Risk | Loans Receivable | South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 3,718	$ 3,070
Percentage of portfolio	15.80%	13.30%
Commercial Banking | Commercial and multifamily real estate | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 2,454	$ 2,441
Percentage of portfolio	10.40%	10.50%
Commercial Banking | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Loans Receivable | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 23,191	$ 22,535
Percentage of portfolio	98.30%	97.40%
Commercial Banking | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 386	$ 540
Percentage of portfolio	1.60%	2.30%
Commercial Banking | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 8	$ 62
Percentage of portfolio	0.10%	0.30%
Commercial Banking | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 27,873	$ 26,972
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Commercial and industrial | Geographic Concentration Risk | Loans Receivable | Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 6,784	$ 6,384
Percentage of portfolio	24.30%	23.70%
Commercial Banking | Commercial and industrial | Geographic Concentration Risk | Loans Receivable | Mid-Atlantic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 2,246	$ 2,121
Percentage of portfolio	8.10%	7.90%
Commercial Banking | Commercial and industrial | Geographic Concentration Risk | Loans Receivable | South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 11,491	$ 12,310
Percentage of portfolio	41.20%	45.60%
Commercial Banking | Commercial and industrial | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 7,352	$ 6,157
Percentage of portfolio	26.40%	22.80%
Commercial Banking | Commercial and industrial | Internal Risk Rating Concentration Risk | Loans Receivable | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 26,096	$ 25,982
Percentage of portfolio	93.60%	96.30%
Commercial Banking | Commercial and industrial | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 1,336	$ 884
Percentage of portfolio	4.80%	3.30%
Commercial Banking | Commercial and industrial | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 441	$ 106
Percentage of portfolio	1.60%	0.40%
Commercial Banking | Small-ticket commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 654	$ 781
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Small-ticket commercial real estate | Geographic Concentration Risk | Loans Receivable | Northeast
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 401	$ 478
Percentage of portfolio	61.30%	61.20%
Commercial Banking | Small-ticket commercial real estate | Geographic Concentration Risk | Loans Receivable | Mid-Atlantic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 25	$ 30
Percentage of portfolio	3.90%	3.80%
Commercial Banking | Small-ticket commercial real estate | Geographic Concentration Risk | Loans Receivable | South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 42	$ 48
Percentage of portfolio	6.40%	6.20%
Commercial Banking | Small-ticket commercial real estate | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 186	$ 225
Percentage of portfolio	28.40%	28.80%
Commercial Banking | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Loans Receivable | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 647	$ 767
Percentage of portfolio	98.90%	98.20%
Commercial Banking | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 3	$ 7
Percentage of portfolio	0.50%	0.90%
Commercial Banking | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 4	$ 7
Percentage of portfolio	0.60%	0.90%