Derivative Financial Statement (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Collateral posted	$ 67.0
Collateral received	46.6
Cash deposits	663.6	$ 79.9
Contractual Notional Amount	20,308.2	23,376.1
Unrecognized loss for all outstanding and terminated cash flow hedges included in accumulated other comprehensive income	553.8		$ 110.6
Cash Flow Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Contractual Notional Amount	4,775.0	4,650.0
Unrecognized loss for all outstanding and terminated cash flow hedges included in accumulated other comprehensive income	553.8	81.1
Total amount of amortization over the next twelve months for all cash flow hedges	19.2
Cash Flow Hedging [Member] | New hedge [Domain]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Instruments, Gain Recognized in Other Comprehensive Income (Loss), Effective Portion	17.1
Cash Flow Hedging [Member] | Expired hedge [Domain]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Notional Amount Expired	5,400.0
Settlement amount	831.6
Loss on Cash Flow Hedge Ineffectiveness	7.7
Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion	823.9
Non-Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Contractual Notional Amount	14,148.2	$ 17,341.1
Non-Hedging Instrument [Member] | Expired hedge [Domain]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Settlement amount	$ 164.4