Commitments (Narrative) (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) railcar	Dec. 31, 2016 USD ($)
Commitments [Line Items]
Financing commitments on which criteria for funding have not been completed	$ 1,200.0	$ 572.0
Financing commitments to trade finance clients that are cancelable only after a notice period, amount	290.2	335.0
Additional funding commitments	1,700.0	1,700.0
Other liabilities	1,496.1	1,897.6
Commitments and investments that qualify for community reinvestment tax credit	105.0	62.0
Deferred Purchase Agreements
Commitments [Line Items]
DPA credit protection provided to clients	2,127.0	1,962.0
DPA credit line agreements net of deferred purchase agreement credit protection	98.0	99.0
Other liabilities	$ 5.8	6.1
Contractual Commitments
Commitments [Line Items]
Railcars | railcar	1,756
Reverse Mortgage
Commitments [Line Items]
FDIC required funding amount of reverse mortgages	$ 65.0	55.0
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
Minimum
Commitments [Line Items]
Percent required of claim amount for loan service	98.00%
Onewest Bank
Commitments [Line Items]
Losses incurred related to indemnification asset	$ 135.0	145.0
Onewest Bank | Maximum
Commitments [Line Items]
Amount of indemnification for losses by FDIC	200.0
Onewest Bank | Minimum
Commitments [Line Items]
Amount FDIC agreed to fund any other draws	200.0
Financial Freedom | Discontinued Operations
Commitments [Line Items]
Financing commitments	$ 36.0	$ 42.0