Derivative Financial Instruments (Derivative Instrument Gains And Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total Return Swap (TRS)
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	$ (2.8)	$ 43.6
Non-Qualifying Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	(28.7)	80.8	$ 92.5
Non-Qualifying Hedges | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	8.5	7.9	4.6
Non-Qualifying Hedges | Interest rate options
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	0.4	0.6	1.6
Non-Qualifying Hedges | Foreign currency forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	(34.2)	26.2	116.5
Non-Qualifying Hedges | Equity Warrants
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	(0.2)	(0.2)	0.2
Non-Qualifying Hedges | Total Return Swap (TRS)
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	(2.8)	43.6	(30.4)
Non-Qualifying Hedges | Interest Rate Lock Commitments
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	0.1	(0.2)	0.0
Non-Qualifying Hedges | Forward sale commitments on agency MBS
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	(0.4)	1.1	0.0
Non-Qualifying Hedges | Credit derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instrument - income statement impact	$ (0.1)	$ 1.8	$ 0.0