Certain Transfers of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows Between Transferor and Transferee, Receipts on Transferor's Interest in Transferred Financial Assets, Other			$ 2	$ 11	$ 12
Total assets		$ 215,543	215,543	205,962
Total liabilities		191,263	191,263	180,808
Long-term Debt	[1],[2]	15,072	15,072	9,785
Gains on sale of OTTI securities		6	6
Debt Securities, Trading, and Equity Securities, FV-NI	[3]	5,506	5,506	5,093
Amortization of Intangible Assets	[4]		18	20
Amortization			73	75	49
Variable Interest Entity, Not Primary Beneficiary [Member]
Investment Tax Credit			89	90	64
Amortization of Intangible Assets			71	70	46
Variable Interest Entity, Primary Beneficiary [Member]
Long-term Debt		161	161	189
Residential Mortgage [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Loans and Leases Receivable, Gain (Loss) on Sales, Net			64	213	$ 331
Transferor's Interests in Transferred Financial Assets, Fair Value				22
Total assets				147
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount				22
Commercial and Corporate Loans [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Loans and Leases Receivable, Gain (Loss) on Sales, Net			35	37
Student Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loans Receivable, Net		165	165	192
Long-term Debt		$ 161	$ 161	$ 189
Student Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Maximum [Member]
Government Guarantee Percent		98.00%	98.00%	98.00%
Total Return Swap [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Derivative Asset, Notional Amount		$ 2,000	$ 2,000	$ 1,700
Debt Securities, Trading, and Equity Securities, FV-NI		$ 2,000	$ 2,000	$ 1,700
Death, Disability, Bankruptcy [Member] | Student Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Maximum [Member]
Government Guarantee Percent		100.00%	100.00%

[1] Includes $289 million and $530 million of long-term debt measured at fair value at December 31, 2018 and 2017, respectively.

[2] Includes debt of consolidated VIEs of $161 million and $189 million at December?31, 2018 and December?31, 2017, respectively.

[3] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,442 million and $1,086 million at December?31, 2018 and December?31, 2017, respectively.

[4] Does not include expense associated with community development investments. See Note 12, “Certain Transfers of Financial Assets and Variable Interest Entities,” for additional information.