Loans (Schedule of Consumer Loan LTV Distributions) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 28,505.3	$ 29,535.9	$ 29,897.0
Single Family Residential
Financing Receivable, Recorded Investment [Line Items]
Loans	5,412.7	5,706.3
Single Family Residential | Greater than 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	197.7	275.9
Single Family Residential | 101% – 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	335.9	462.0
Single Family Residential | 80% – 100%
Financing Receivable, Recorded Investment [Line Items]
Loans	750.0	855.2
Single Family Residential | Less than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans	4,128.3	4,110.3
Single Family Residential | Not Applicable
Financing Receivable, Recorded Investment [Line Items]
Loans	0.8	2.9
Single Family Residential | Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,488.8	1,749.1
Single Family Residential | Covered Loans | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,970.8	2,165.6
Single Family Residential | Covered Loans | Greater than 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	2.7	2.2
Single Family Residential | Covered Loans | Greater than 125% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	186.7	261.4
Single Family Residential | Covered Loans | 101% – 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	6.6	4.7
Single Family Residential | Covered Loans | 101% – 125% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	323.0	443.7
Single Family Residential | Covered Loans | 80% – 100%
Financing Receivable, Recorded Investment [Line Items]
Loans	104.8	226.6
Single Family Residential | Covered Loans | 80% – 100% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	585.0	588.1
Single Family Residential | Covered Loans | Less than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans	1,374.7	1,515.6
Single Family Residential | Covered Loans | Less than 80% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	876.1	872.4
Single Family Residential | Covered Loans | Not Applicable
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Single Family Residential | Covered Loans | Not Applicable | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Single Family Residential | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	1,945.6	1,782.4
Single Family Residential | Non-covered Loans | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	7.5	9.2
Single Family Residential | Non-covered Loans | Greater than 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	8.3	12.3
Single Family Residential | Non-covered Loans | Greater than 125% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Single Family Residential | Non-covered Loans | 101% – 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	6.3	13.6
Single Family Residential | Non-covered Loans | 101% – 125% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Single Family Residential | Non-covered Loans | 80% – 100%
Financing Receivable, Recorded Investment [Line Items]
Loans	60.2	40.5
Single Family Residential | Non-covered Loans | 80% – 100% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Single Family Residential | Non-covered Loans | Less than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans	1,870.0	1,713.1
Single Family Residential | Non-covered Loans | Less than 80% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	7.5	9.2
Single Family Residential | Non-covered Loans | Not Applicable
Financing Receivable, Recorded Investment [Line Items]
Loans	0.8	2.9
Single Family Residential | Non-covered Loans | Not Applicable | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Reverse Mortgage
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	858.9
Loans transferred to AHFS	862.1
Reverse Mortgage | Greater than 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	43.2
Reverse Mortgage | 101% – 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	21.8
Reverse Mortgage | 80% – 100%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	73.8
Reverse Mortgage | Less than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	720.1
Reverse Mortgage | Not Applicable
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Reverse Mortgage | Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	431.2
Loans transferred to AHFS	412.4
Reverse Mortgage | Covered Loans | Greater than 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.6
Reverse Mortgage | Covered Loans | 101% – 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	1.2
Reverse Mortgage | Covered Loans | 80% – 100%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	24.0
Reverse Mortgage | Covered Loans | Less than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	405.4
Reverse Mortgage | Covered Loans | Not Applicable
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Reverse Mortgage | Non-covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	368.7
Reverse Mortgage | Non-covered Loans | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	59.0
Reverse Mortgage | Non-covered Loans | Greater than 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	8.8
Reverse Mortgage | Non-covered Loans | Greater than 125% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	33.8
Reverse Mortgage | Non-covered Loans | 101% – 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	12.7
Reverse Mortgage | Non-covered Loans | 101% – 125% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	7.9
Reverse Mortgage | Non-covered Loans | 80% – 100%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	42.3
Reverse Mortgage | Non-covered Loans | 80% – 100% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	7.5
Reverse Mortgage | Non-covered Loans | Less than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	304.9
Reverse Mortgage | Non-covered Loans | Less than 80% | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	9.8
Reverse Mortgage | Non-covered Loans | Not Applicable
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Reverse Mortgage | Non-covered Loans | Not Applicable | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	0.0	0.0
Consumer Banking
Financing Receivable, Recorded Investment [Line Items]
Loans	5,412.7	6,565.2
Consumer Banking | Greater than 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	197.7	319.1
Consumer Banking | 101% – 125%
Financing Receivable, Recorded Investment [Line Items]
Loans	335.9	483.8
Consumer Banking | 80% – 100%
Financing Receivable, Recorded Investment [Line Items]
Loans	750.0	929.0
Consumer Banking | Less than 80%
Financing Receivable, Recorded Investment [Line Items]
Loans	4,128.3	4,830.4
Consumer Banking | Not Applicable
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0.8	$ 2.9