Loans - Commercial Banking: Risk Profile by Geographic Region and Internal Risk Rating (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 244,302	$ 245,586	$ 234,603
Receivables Acquired with Deteriorated Credit Quality [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	12,895	15,071
Commercial Banking
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 67,672	$ 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	$ 524	$ 613
Commercial Banking | Commercial and multifamily real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 27,428	$ 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	$ 26	$ 28
Commercial Banking | Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 39,801	$ 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	$ 498	$ 585
Commercial Banking | Small-ticket commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 443	$ 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	$ 24,773	$ 25,640
Percentage of portfolio	36.60%	38.30%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | Mid-Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 7,124	$ 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	$ 19,052	$ 19,259
Percentage of portfolio	28.20%	28.80%
Commercial Banking | Loans Receivable | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 16,723	$ 15,527
Percentage of portfolio	24.70%	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	$ 524	$ 613
Percentage of portfolio	0.80%	0.90%
Commercial Banking | Loans Receivable | Internal Risk Rating Concentration Risk | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 63,802	$ 62,828
Percentage of portfolio	94.30%	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	$ 2,660	$ 2,453
Percentage of portfolio	3.90%	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	$ 686	$ 1,022
Percentage of portfolio	1.00%	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	$ 15,636	$ 15,714
Percentage of portfolio	57.00%	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	$ 3,212	$ 3,024
Percentage of portfolio	11.70%	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	$ 3,924	$ 4,032
Percentage of portfolio	14.30%	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	$ 4,656	$ 3,839
Percentage of portfolio	17.00%	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	$ 26	$ 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	$ 26,930	$ 26,309
Percentage of portfolio	98.20%	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	$ 438	$ 242
Percentage of portfolio	1.60%	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	$ 34	$ 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	$ 8,863	$ 9,628
Percentage of portfolio	22.30%	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	$ 3,896	$ 3,450
Percentage of portfolio	9.80%	8.70%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | South
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 15,100	$ 15,193
Percentage of portfolio	37.90%	38.10%
Commercial Banking | Loans Receivable | Commercial and industrial | Geographic Concentration Risk | Other
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 11,942	$ 11,553
Percentage of portfolio	30.00%	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	$ 498	$ 585
Percentage of portfolio	1.30%	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	$ 36,439	$ 36,046
Percentage of portfolio	91.50%	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	$ 2,221	$ 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	$ 643	$ 988
Percentage of portfolio	1.60%	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	$ 274	$ 298
Percentage of portfolio	61.90%	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	3.60%	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	$ 28	$ 34
Percentage of portfolio	6.30%	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	$ 125	$ 135
Percentage of portfolio	28.20%	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
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	$ 433	$ 473
Percentage of portfolio	97.80%	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	$ 9	$ 4
Percentage of portfolio	2.00%	0.80%
Operating Segments [Member] | Commercial Banking
Loans and Leases Receivable Disclosure [Line Items]
Loans held for investment	$ 67,672	$ 66,916	$ 66,202