Investment Securities (Mortgage-backed Asset Securities Table) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 5,963.4	$ 5,991.4	$ 6,777.0	$ 6,766.5
Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	204.2
Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	355.4	411.2
Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	38.9	36.6
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34.8	49.6
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	429.1	497.4
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	204.5	131.2
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	301.0	236.9
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	505.5	368.1
Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	934.6	865.5
Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	518.6	522.2
Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	430.0	289.4
Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	194.2	163.8
Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,142.8	975.4
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,077.4	1,840.9
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	4,746.7	4,638.0	$ 4,774.0	$ 4,982.2
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	355.4	411.2
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	38.9	36.6
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34.8	49.6
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	429.1	497.4
Level 2 Inputs | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	204.5	131.2
Level 2 Inputs | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	301.0	236.9
Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	505.5	368.1
Level 2 Inputs | Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	934.6	865.5
Level 2 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	518.6	522.2
Level 2 Inputs | Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	430.0	289.4
Level 2 Inputs | Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	186.8	163.8
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,135.4	975.4
Level 2 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,070.0	1,840.9
Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0.0	0.0
Level 3 Inputs | Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	7.4	0.0
Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	7.4	0.0
Level 3 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 7.4	$ 0.0
Maximum | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Loans and Leases Receivable, Ratio of Nonperforming Loans to All Loans	1.00%