Loans - Commercial Banking: Risk Profile by Geographic Region and Internal Risk Rating (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 229,851	$ 208,316	$ 197,199
Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 63,266	$ 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	$ 24,399	$ 21,997
Percentage of portfolio	38.60%	43.20%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | Mid-Atlantic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 5,832	$ 4,642
Percentage of portfolio	9.20%	9.10%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 19,350	$ 15,428
Percentage of portfolio	30.60%	30.30%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 13,685	$ 8,823
Percentage of portfolio	21.60%	17.40%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 59,743	$ 49,092
Percentage of portfolio	94.40%	96.50%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 2,015	$ 1,431
Percentage of portfolio	3.20%	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	$ 550	$ 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	$ 25,518	$ 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	$ 15,949	$ 15,135
Percentage of portfolio	62.50%	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	$ 2,797	$ 2,491
Percentage of portfolio	11.00%	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	$ 4,070	$ 3,070
Percentage of portfolio	15.90%	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	$ 2,702	$ 2,441
Percentage of portfolio	10.60%	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	$ 25,130	$ 22,489
Percentage of portfolio	98.50%	97.20%
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	$ 350	$ 540
Percentage of portfolio	1.40%	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	$ 7	$ 62
Percentage of portfolio	0.00%	0.30%
Commercial Banking | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 37,135	$ 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	$ 8,074	$ 6,384
Percentage of portfolio	21.80%	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	$ 3,010	$ 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	$ 15,240	$ 12,310
Percentage of portfolio	41.00%	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	$ 10,811	$ 6,157
Percentage of portfolio	29.10%	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	$ 34,008	$ 25,836
Percentage of portfolio	91.60%	95.80%
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	$ 1,662	$ 884
Percentage of portfolio	4.50%	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	$ 538	$ 106
Percentage of portfolio	1.40%	0.40%
Commercial Banking | Small-ticket commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 613	$ 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	$ 376	$ 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	4.10%	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	$ 40	$ 48
Percentage of portfolio	6.50%	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	$ 172	$ 225
Percentage of portfolio	28.10%	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	$ 605	$ 767
Percentage of portfolio	98.70%	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	$ 5	$ 7
Percentage of portfolio	0.80%	0.90%
Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 19,518	$ 23,500
Acquired Loans | Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	958	192
Acquired Loans | Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 958	$ 192
Percentage of portfolio	1.50%	0.40%
Acquired Loans | Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 128	$ 171
Acquired Loans | Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	793	18
Acquired Loans | Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	37	3
Acquired Loans | Commercial Banking | Commercial and multifamily real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	31	46
Acquired Loans | Commercial Banking | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 31	$ 46
Percentage of portfolio	0.10%	0.20%
Acquired Loans | Commercial Banking | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 927	$ 146
Acquired Loans | Commercial Banking | Commercial and industrial | Internal Risk Rating Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 927	$ 146
Percentage of portfolio	2.50%	0.50%
Acquired Loans | Commercial Banking | Small-ticket commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 0	$ 0
Acquired Loans | Commercial Banking | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Loans Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 0	$ 0
Percentage of portfolio	0.00%	0.00%