Commitments (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) railcar	Dec. 31, 2016 USD ($)
Commitments [Line Items]
Financing commitments on which criteria for funding have not been completed	$ 881,300,000	$ 572,000,000
Financing commitments which are only cancellable under notice period	190,000,000	335,000,000
Undrawn financing commitments with no contractual obligation to lend	1,600,000,000	1,700,000,000
Other liabilities	1,437,100,000	1,897,600,000
Commitments to investments in affordable housing investments and other investments qualifying for community reinvestment tax credits	67,000,000	62,000,000
Deferred Purchase Agreements
Commitments [Line Items]
DPA credit protection provided to clients	1,979,000,000	1,962,000,000
DPA credit line agreements net of deferred purchase agreement credit protection	89,000,000	99,000,000
Other liabilities	$ 5,300,000	6,100,000
Purchase Commitments
Commitments [Line Items]
Railcars | railcar	1,550
Minimum
Commitments [Line Items]
Percent required of claim amount for loan service	98.00%
Maximum
Commitments [Line Items]
Typical notice period	90 days
Maximum | Deferred Purchase Agreements
Commitments [Line Items]
DPA credit line agreements, cancellation notice period	90 days
OneWest Bank
Commitments [Line Items]
Losses incurred related to indemnification asset	$ 134,000,000	145,000,000
OneWest Bank | Minimum
Commitments [Line Items]
Amount FDIC agreed to fund any other draws	200,000,000
OneWest Bank | Maximum
Commitments [Line Items]
Amount of indemnification for losses by FDIC	200,000,000
Reverse Mortgage
Commitments [Line Items]
Exposure for additional draws on loan commitments	66,000,000	55,000,000
Discontinued Operation | Financial Freedom
Commitments [Line Items]
Financing commitments	$ 34,000,000	$ 42,000,000