Commitments, Contingencies, Guarantees, and Others - Litigation (Details) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Jul. 31, 2012 USD ($)	Feb. 28, 2009 USD ($) Contract MortgageLoan	Jul. 31, 2012 USD ($) trust summon	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss				$ 550
Pending Litigation | Interchange Litigation
Loss Contingencies [Line Items]
Litigation Settlement, Attributable to Reporting Entity and Third Party, Percent of Transactions	0.10%
Litigation settlement, attributable to reporting entity and third party	$ 6,600
Litigation settlement, attributable to reporting entity and third party, period of payment of settlement	8 months
GreenPoint Subsidiary | Pending Litigation | U.S. Bank Litigation
Loss Contingencies [Line Items]
Number of contracts breached | Contract		2
Number of mortgage loans sold to third party under litigation | MortgageLoan		30,000
Mortgage loans sold to third party, face amount under litigation		$ 1,800
GreenPoint Subsidiary | Pending Litigation | FHFA Litigation
Loss Contingencies [Line Items]
Mortgage loans sold to third party, face amount under litigation	$ 3,400		$ 3,400
Number of summons filed | summon			3
Number of residential mortgage backed securities trusts | trust			3
Representation and Warranty Liability [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual, Payments				540
Loss Contingency, Loss in Period				$ 169