Loans - Commercial Banking: Risk Profile by Geographic Region and Internal Risk Rating (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 245,586	$ 229,851	$ 208,316
Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	15,071	19,518
Commercial Banking
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 66,916	$ 63,266
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	$ 613	$ 958
Commercial Banking | Commercial and multifamily real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 26,609	$ 25,518
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	$ 28	$ 31
Commercial Banking | Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 39,824	$ 37,135
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	$ 585	$ 927
Commercial Banking | Small-ticket commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 483	$ 613
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	$ 25,640	$ 24,399
Percentage of portfolio	38.30%	38.60%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | Mid-Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 6,490	$ 5,832
Percentage of portfolio	9.70%	9.20%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 19,259	$ 19,350
Percentage of portfolio	28.80%	30.60%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 15,527	$ 13,685
Percentage of portfolio	23.20%	21.60%
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	$ 613	$ 958
Percentage of portfolio	0.90%	1.50%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 62,828	$ 59,743
Percentage of portfolio	93.90%	94.40%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Noncriticized | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 346	$ 128
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Criticized | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 2,453	$ 2,015
Percentage of portfolio	3.70%	3.20%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Criticized | Criticized performing | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 247	$ 793
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Criticized | Criticized nonperforming
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 1,022	$ 550
Percentage of portfolio	1.50%	0.90%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Criticized | Criticized nonperforming | Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 20	$ 37
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Geographic Concentration Risk | Northeast
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 15,714	$ 15,949
Percentage of portfolio	59.00%	62.50%
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	$ 3,024	$ 2,797
Percentage of portfolio	11.40%	11.00%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 4,032	$ 4,070
Percentage of portfolio	15.20%	15.90%
Commercial Banking | Loans Receivable | Commercial and multifamily real estate | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,839	$ 2,702
Percentage of portfolio	14.40%	10.60%
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	$ 28	$ 31
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	$ 26,309	$ 25,130
Percentage of portfolio	98.90%	98.50%
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	$ 242	$ 350
Percentage of portfolio	0.90%	1.40%
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	$ 30	$ 7
Percentage of portfolio	0.10%	0.00%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | Northeast
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 9,628	$ 8,074
Percentage of portfolio	24.20%	21.80%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | Mid-Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 3,450	$ 3,010
Percentage of portfolio	8.70%	8.10%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 15,193	$ 15,240
Percentage of portfolio	38.10%	41.00%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 11,553	$ 10,811
Percentage of portfolio	29.00%	29.10%
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	$ 585	$ 927
Percentage of portfolio	1.50%	2.50%
Commercial Banking | Loans Receivable | Commercial and industrial | Internal Risk Rating Concentration Risk | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 36,046	$ 34,008
Percentage of portfolio	90.50%	91.60%
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	$ 2,205	$ 1,662
Percentage of portfolio	5.50%	4.50%
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	$ 988	$ 538
Percentage of portfolio	2.50%	1.40%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Geographic Concentration Risk | Northeast
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 298	$ 376
Percentage of portfolio	61.70%	61.30%
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	$ 25
Percentage of portfolio	3.30%	4.10%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 34	$ 40
Percentage of portfolio	7.00%	6.50%
Commercial Banking | Loans Receivable | Small-ticket commercial real estate | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 135	$ 172
Percentage of portfolio	28.00%	28.10%
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	$ 473	$ 605
Percentage of portfolio	97.90%	98.70%
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	$ 6	$ 3
Percentage of portfolio	1.30%	0.50%
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	$ 4	$ 5
Percentage of portfolio	0.80%	0.80%