Loans - Commercial Banking: Risk Profile by Geographic Region and Internal Risk Rating (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 240,588	$ 245,586	$ 227,613
Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	14,102	15,071
Commercial Banking
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 67,320	$ 66,916
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 594	$ 613
Commercial Banking | Commercial and multifamily real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 27,218	$ 26,609
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Commercial and multifamily real estate | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 31	$ 28
Commercial Banking | Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 39,638	$ 39,824
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Commercial and industrial | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 563	$ 585
Commercial Banking | Small-ticket commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 464	$ 483
Percentage of portfolio	100.00%	100.00%
Commercial Banking | Small-ticket commercial real estate | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 0	$ 0
Commercial Banking | Loans Receivable | Geographic Concentration Risk | Northeast
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 25,310	$ 25,640
Percentage of portfolio	37.60%	38.30%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | Mid-Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 7,076	$ 6,490
Percentage of portfolio	10.50%	9.70%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 18,883	$ 19,259
Percentage of portfolio	28.10%	28.80%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 16,051	$ 15,527
Percentage of portfolio	23.80%	23.20%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 594	$ 613
Percentage of portfolio	0.90%	0.90%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 63,390	$ 62,828
Percentage of portfolio	94.20%	93.90%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Criticized | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 2,492	$ 2,453
Percentage of portfolio	3.70%	3.70%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Criticized | Criticized nonperforming
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 844	$ 1,022
Percentage of portfolio	1.20%	1.50%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Geographic Concentration Risk | Northeast
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 15,580	$ 15,714
Percentage of portfolio	57.20%	59.00%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Geographic Concentration Risk | Mid-Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,260	$ 3,024
Percentage of portfolio	12.00%	11.40%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,917	$ 4,032
Percentage of portfolio	14.40%	15.20%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 4,461	$ 3,839
Percentage of portfolio	16.40%	14.40%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 31	$ 28
Percentage of portfolio	0.10%	0.10%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 26,881	$ 26,309
Percentage of portfolio	98.80%	98.90%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Criticized | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 271	$ 242
Percentage of portfolio	1.00%	0.90%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Internal Risk Rating Concentration Risk | Criticized | Criticized nonperforming
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 35	$ 30
Percentage of portfolio	0.10%	0.10%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | Northeast
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 9,444	$ 9,628
Percentage of portfolio	23.80%	24.20%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | Mid-Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,800	$ 3,450
Percentage of portfolio	9.60%	8.70%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 14,934	$ 15,193
Percentage of portfolio	37.70%	38.10%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 11,460	$ 11,553
Percentage of portfolio	28.90%	29.00%
Commercial Banking | Loans Receivable | Commercial and industrial | Internal Risk Rating Concentration Risk | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 563	$ 585
Percentage of portfolio	1.40%	1.50%
Commercial Banking | Loans Receivable | Commercial and industrial | Internal Risk Rating Concentration Risk | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 36,054	$ 36,046
Percentage of portfolio	91.00%	90.50%
Commercial Banking | Loans Receivable | Commercial and industrial | Internal Risk Rating Concentration Risk | Criticized | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 2,220	$ 2,205
Percentage of portfolio	5.60%	5.50%
Commercial Banking | Loans Receivable | Commercial and industrial | Internal Risk Rating Concentration Risk | Criticized | Criticized nonperforming
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 801	$ 988
Percentage of portfolio	2.00%	2.50%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Geographic Concentration Risk | Northeast
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 286	$ 298
Percentage of portfolio	61.60%	61.70%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Geographic Concentration Risk | Mid-Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 16	$ 16
Percentage of portfolio	3.50%	3.30%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 32	$ 34
Percentage of portfolio	6.90%	7.00%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 130	$ 135
Percentage of portfolio	28.00%	28.00%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 0	$ 0
Percentage of portfolio	0.00%	0.00%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 455	$ 473
Percentage of portfolio	98.10%	97.90%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Criticized | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 1	$ 6
Percentage of portfolio	0.20%	1.30%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Internal Risk Rating Concentration Risk | Criticized | Criticized nonperforming
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 8	$ 4
Percentage of portfolio	1.70%	0.80%