Loans Held-for-Investment (Troubled Debt Restructuring, New ) (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan	Jun. 30, 2016 USD ($) loan	Jun. 30, 2017 USD ($) loan	Jun. 30, 2016 USD ($) loan
Troubled Debt Restructurings [Line Items]
Number of Accounts \| loan	28		28	43	128
Pre-Modification Unpaid Principal Balance	$ 2.0		$ 3.0	$ 3.0	$ 12.0
Post-Modification Unpaid Principal Balance	2.0		3.0	3.0	11.0
Increase in Allowance at Modification	0.0		$ 0.0	0.0	$ 0.0
Unpaid principal balance	$ 63.0	$ 75.0		$ 63.0
Residential first mortgage
Troubled Debt Restructurings [Line Items]
Number of Accounts \| loan	6		3	8	16
Pre-Modification Unpaid Principal Balance	$ 1.0		$ 1.0	$ 1.0	$ 3.0
Post-Modification Unpaid Principal Balance	1.0		1.0	1.0	4.0
Increase in Allowance at Modification	0.0		$ 0.0	0.0	$ 0.0
Unpaid principal balance	$ 35.0	46.0		$ 35.0
Number of loans modified in previous 12 months that have defaulted \| loan	1		1	1	1
Modifications subsequent to default	$ 1.0		$ 1.0	$ 1.0	$ 1.0
Home equity
Troubled Debt Restructurings [Line Items]
Number of Accounts \| loan	21		25	34	111
Pre-Modification Unpaid Principal Balance	$ 1.0		$ 2.0	$ 2.0	$ 7.0
Post-Modification Unpaid Principal Balance	1.0		2.0	2.0	6.0
Increase in Allowance at Modification	0.0		$ 0.0	0.0	$ 0.0
Unpaid principal balance	$ 28.0	$ 29.0		28.0
Number of loans modified in previous 12 months that have defaulted \| loan			4		4
Other consumer
Troubled Debt Restructurings [Line Items]
Number of Accounts \| loan		1
Pre-Modification Unpaid Principal Balance		$ 0.0		0.0
Post-Modification Unpaid Principal Balance		0.0		0.0
Increase in Allowance at Modification		$ 0.0		$ 0.0
Commercial real estate
Troubled Debt Restructurings [Line Items]
Number of Accounts \| loan				1
Commercial and industrial
Troubled Debt Restructurings [Line Items]
Number of Accounts \| loan					1
Pre-Modification Unpaid Principal Balance					$ 2.0
Post-Modification Unpaid Principal Balance					1.0
Increase in Allowance at Modification					$ 0.0

Amount of other addition (reduction) in allowance reserve for credit loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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