Certain Transfers of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Assets		$ 207,505		$ 207,505		$ 205,962
Total liabilities		183,189		183,189		180,808
Long-term Debt	[1]	11,995		11,995		9,785
Gains on sale of OTTI securities		6		6
Trading Securities	[2]	5,050		5,050		5,093
Investment Tax Credit			$ 19
Amortization of Intangible Assets	[3]			11	$ 10
Amortization		17	15	32	28
Variable Interest Entity, Not Primary Beneficiary [Member]
Investment Tax Credit				38	35
Amortization of Intangible Assets		16	14	31	27
Variable Interest Entity, Primary Beneficiary [Member]
Long-term Debt		174		174		189
Residential Mortgage [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Loans and Leases Receivable, Gain (Loss) on Sales, Net		19	83	7	79
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		5	$ 3	14	$ 17
Student Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loans Receivable, Net		177		177		192
Long-term Debt		$ 174		$ 174		$ 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		$ 1,600		$ 1,600		$ 1,700
Trading Securities		$ 1,600		$ 1,600		$ 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 $174 million and $189 million at June 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 $1,160 million and $1,086 million at June 30, 2018 and December 31, 2017, respectively.

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