Certain Transfers of Financial Assets and Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2016
Cash Flows Between Transferor and Transferee, Receipts on Transferor's Interest in Transferred Financial Assets, Other		$ 4	$ 4	$ 9	$ 10
Assets		208,252		208,252			$ 204,875
Liabilities		183,730		183,730			181,257
Long-term Debt	[1]	11,280		11,280			11,748
Potential Loss on Securitization of Loans		338		338
Derivative Asset, Notional Amount		132,264		$ 132,264			127,456
Document Period End Date				Sep. 30, 2017
Trading assets	[2]	6,318		$ 6,318			6,067
Other Assets		7,225		7,225			6,405
Affordable Housing Tax Credits and Other Tax Benefits, Amount		27	27	77	65
Amortization Method Qualified Affordable Housing Project Investments, Amortization		27	23	76	62
Amortization of Intangible Assets	[3]			16	6
Amortization		22	14	49	35
Variable Interest Entity, Not Primary Beneficiary [Member] | Community Development Investments [Member]
Investment Tax Credit		25	18	60	46
Amortization of Intangible Assets		19	13	45	33
Variable Interest Entity, Primary Beneficiary [Member]
Long-term Debt		195		195			222
Residential Mortgage [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Loans and Leases Receivable, Gain (Loss) on Sales, Net		73	$ 131	152	$ 288
Transferor's Interests in Transferred Financial Assets, Fair Value		24		24			30
Assets		161		161			203
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		24		24			30
Commercial and Corporate Loans [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Loans and Leases Receivable, Gain (Loss) on Sales, Net		9		33
Student Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Loans Receivable, Net		198		198			225
Long-term Debt		$ 195		$ 195			222
Student Loans [Member] | Variable Interest Entity, Primary Beneficiary [Member] | Maximum [Member]
Government Guarantee Percent		98.00%		98.00%
Total Return Swap [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Derivative Asset, Notional Amount		$ 2,500		$ 2,500			2,100
Trading assets		2,500		2,500			2,100
Community Development Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Assets		2,300		2,300			1,700
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		604		604			562
Real Estate Variable Interest Entity Borrowings		244		244			200
Limited Partner [Member] | Community Development Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Other Assets		1,029		1,029			780
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		1,311		1,311			1,076
Loans Issued by the Company to the Limited Partnerships		$ 338		$ 338			$ 306
Consumer Portfolio Segment [Member] | Asset-backed Securities, Securitized Loans and Receivables [Member]
Proceeds from Securitizations of Consumer Loans						$ 1,000
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 $195 million and $222 million at September 30, 2017 and December 31, 2016, respectively.

[2] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,043 million and $1,437 million at September 30, 2017 and December 31, 2016, respectively.

[3] Does not include expense associated with non-qualified community development investments. See Note 8, "Certain Transfers of Financial Assets and Variable Interest Entities," for additional information.