Variable Interest Entities and Securitizations - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Funded HELOCs advances	$ 30	$ 30
Unfunded commitment on residual interests on trusts	4	5
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	971	1,043
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	1,674	1,120
Amortization Method Qualified Affordable Housing Project Investments, Amortization	582	393
Affordable Housing Tax Credits And Other Tax Benefits, Amount	504	444
Amortization Method Qualified Affordable Housing Project Investments	3,900	3,800
Qualified Affordable Housing Project Investments, Commitment	1,400	1,200
Variable Interest Entity, Consolidated, Carrying Amount, Assets	36,700	34,651
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	4,948	4,250
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 5,550	5,325
Minimum
Variable Interest Entity [Line Items]
Affordable Housing Tax Credits Commitment, Year to be Paid	2018
Maximum
Variable Interest Entity [Line Items]
Affordable Housing Tax Credits Commitment, Year to be Paid	2020
Affordable housing entities
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	$ 1,284	1,093
Total assets of the unconsolidated VIE investment funds	11,500	11,500
Variable Interest Entity, Consolidated, Carrying Amount, Assets	226	174
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	4,175	3,862
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	4,175	3,862
Entities that provide capital to low-income and rural communities
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets	1,498	927
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	0	0
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	0	0
Other
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets	0	0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	318	187
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	318	187
GreenPoint Manufactured Housing
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	10	8
GPMH [Member]
Variable Interest Entity [Line Items]
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	283
Variable Interest Entity, Not Primary Beneficiary | Option- ARM
Variable Interest Entity [Line Items]
Continuing Involvement with Derecognized Transferred Financial Assets, Liabilities Incurred	1,224	1,499
Continuing Involvement with Derecognized Transferred Financial Assets, Amount Outstanding	1,266	1,549
Variable Interest Entity, Not Primary Beneficiary | GreenPoint HELOCs
Variable Interest Entity [Line Items]
Continuing Involvement with Derecognized Transferred Financial Assets, Liabilities Incurred	42	56
Continuing Involvement with Derecognized Transferred Financial Assets, Amount Outstanding	35	50
Variable Interest Entity, Not Primary Beneficiary | GreenPoint Manufactured Housing
Variable Interest Entity [Line Items]
Continuing Involvement with Derecognized Transferred Financial Assets, Amount Outstanding		702
Letters of credit funded	75	85
Variable Interest Entity, Not Primary Beneficiary | GPMH [Member]
Variable Interest Entity [Line Items]
Continuing Involvement with Derecognized Transferred Financial Assets, Liabilities Incurred	508	697
Continuing Involvement with Derecognized Transferred Financial Assets, Amount Outstanding	$ 511	$ 702