Certain Transfers of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Assets		$ 211,276		$ 211,276		$ 205,962
Total liabilities		187,137		187,137		180,808
Long-term Debt	[1]	14,289		14,289		9,785
Gains on sale of OTTI securities		6		6
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	5,676		5,676		5,093
Investment Tax Credit			$ 25
Amortization of Intangible Assets	[3]			13	$ 16
Amortization		19	22	51	49
Variable Interest Entity, Not Primary Beneficiary [Member]
Investment Tax Credit				62	60
Amortization of Intangible Assets		19	19	49	45
Variable Interest Entity, Primary Beneficiary [Member]
Long-term Debt		168		168		189
Residential Mortgage [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Loans and Leases Receivable, Gain (Loss) on Sales, Net		46	73	53	152
Transferor's Interests in Transferred Financial Assets, Fair Value						22
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		8	$ 9	22	$ 33
Student Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loans Receivable, Net		171		171		192
Long-term Debt		$ 168		$ 168		$ 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		$ 1,900		$ 1,900		$ 1,700
Debt Securities, Trading, and Equity Securities, FV-NI		$ 1,900		$ 1,900		$ 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 debt of consolidated VIEs of $168 million and $189 million at September 30, 2018 and December 31, 2017, respectively.

[2] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,362 million and $1,086 million at September 30, 2018 and December 31, 2017, respectively.

[3] Does not include expense associated with community development investments. See Note 10, "Certain Transfers of Financial Assets and Variable Interest Entities," for additional information.