Borrowings (Schedule of Long-Term Borrowings) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term borrowings	$ 8,621.4	$ 14,935.5
Parent Company [Member]
Debt Instrument [Line Items]
Long-term borrowings	4,545.1
Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term borrowings	4,076.3
Senior Unsecured Borrowings [Member]
Debt Instrument [Line Items]
Long-term borrowings	4,545.1	10,599.0
Senior Unsecured Borrowings [Member] | Parent Company [Member]
Debt Instrument [Line Items]
Long-term borrowings	4,545.1
Senior Unsecured Borrowings [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term borrowings	0.0
Structured Financings [Member]
Debt Instrument [Line Items]
Long-term borrowings	1,680.8	1,925.7
Structured Financings [Member] | Parent Company [Member]
Debt Instrument [Line Items]
Long-term borrowings	0.0
Structured Financings [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term borrowings	1,680.8
FHLB Advances [Member]
Debt Instrument [Line Items]
Long-term borrowings	2,395.5	$ 2,410.8
FHLB Advances [Member] | Parent Company [Member]
Debt Instrument [Line Items]
Long-term borrowings	0.0
FHLB Advances [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 2,395.5