Loans - Commercial Banking: Risk Profile by Geographic Region and Internal Risk Rating (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	$ 208,316	$ 197,199	$ 205,889
Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	50,890	45,011
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	21,997	20,956
Percentage of portfolio	43.20%	46.50%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | Mid-Atlantic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	4,642	3,812
Percentage of portfolio	9.10%	8.50%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	15,428	13,540
Percentage of portfolio	30.30%	30.10%
Commercial Banking | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	8,823	6,703
Percentage of portfolio	17.40%	14.90%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	49,284	43,823
Percentage of portfolio	96.90%	97.40%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	1,431	1,039
Percentage of portfolio	2.80%	2.30%
Commercial Banking | Internal Risk Rating Concentration Risk | Loans Receivable | Criticized | Criticized nonperforming
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	175	149
Percentage of portfolio	0.30%	0.30%
Commercial Banking | Commercial and multifamily real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	23,137	20,750
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	15,135	14,551
Percentage of portfolio	65.40%	70.10%
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	2,491	2,194
Percentage of portfolio	10.80%	10.60%
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	3,070	2,541
Percentage of portfolio	13.30%	12.20%
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	2,441	1,464
Percentage of portfolio	10.50%	7.10%
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	22,535	20,276
Percentage of portfolio	97.40%	97.70%
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	540	421
Percentage of portfolio	2.30%	2.10%
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	62	53
Percentage of portfolio	0.30%	0.20%
Commercial Banking | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	26,972	23,309
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	6,384	5,823
Percentage of portfolio	23.70%	25.00%
Commercial Banking | Commercial and industrial | Geographic Concentration Risk | Loans Receivable | Mid-Atlantic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	2,121	1,585
Percentage of portfolio	7.90%	6.80%
Commercial Banking | Commercial and industrial | Geographic Concentration Risk | Loans Receivable | South
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	12,310	10,941
Percentage of portfolio	45.60%	46.90%
Commercial Banking | Commercial and industrial | Geographic Concentration Risk | Loans Receivable | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	6,157	4,960
Percentage of portfolio	22.80%	21.30%
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	25,982	22,606
Percentage of portfolio	96.30%	97.00%
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	884	610
Percentage of portfolio	3.30%	2.60%
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	106	93
Percentage of portfolio	0.40%	0.40%
Commercial Banking | Small-ticket commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	781	952
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	478	582
Percentage of portfolio	61.20%	61.10%
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	30	33
Percentage of portfolio	3.80%	3.50%
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	48	58
Percentage of portfolio	6.20%	6.10%
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	225	279
Percentage of portfolio	28.80%	29.30%
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	767	941
Percentage of portfolio	98.20%	98.90%
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	7	8
Percentage of portfolio	0.90%	0.80%
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	$ 7	$ 3
Percentage of portfolio	0.90%	0.30%