Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivative [Line Items]
Derivative assets recorded on the consolidated balance sheet, reduced as a result of master netting agreements	$ 900,000,000		$ 900,000,000
Derivative liabilities recorded on the consolidated balance sheet, reduced as a result of master netting agreements					$ 1,700,000,000
Derivative asset, fair value, amount offset against collateral	203,000,000		203,000,000		877,200,000
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 21	237,800,000		237,800,000		336,400,000
This amount represents additional cash collateral received from derivative counterparties not offset against derivative assets	43,000,000		43,000,000
Gains or losses reclassified into earnings		$ 0	$ 0
Maximum length of time over which exposure was being hedged			23 months
Aggregate fair value of all derivative instruments with credit-risk-related contingent features that are in a liability position	240,400,000		$ 240,400,000		358,200,000
Collateral deposited with derivative counterparties for derivatives instruments with credit-risk-related contingent features that are in a liability position	190,100,000		190,100,000		317,500,000
Termination payments that could have been required for derivative instruments with credit-risk-related contingent features	50,300,000		50,300,000		40,700,000
Ineffectiveness or changes in the fair value of hedged items recognized in earnings for fair value hedges	0	0	0	$ 0
Ineffectiveness recognized in earnings for cash flow hedges	0	0	0	0
Ineffectiveness from net investment hedges	0	$ 0	0	$ 0
Net Investment Hedges
Derivative [Line Items]
Derivative assets recorded on the consolidated balance sheet, reduced as a result of master netting agreements	1,800,000,000		1,800,000,000
Derivative liabilities recorded on the consolidated balance sheet, reduced as a result of master netting agreements					1,700,000,000
Derivative asset, fair value, amount offset against collateral	617,900,000		617,900,000		461,300,000
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 21	334,300,000		334,300,000		722,100,000
This amount represents additional cash collateral received from derivative counterparties not offset against derivative assets	235,500,000		235,500,000		70,800,000
This amount represents additional cash collateral deposited with derivative counterparties not offset against derivative liabilities	$ 405,000,000		$ 405,000,000		$ 324,500,000
Client Related and Trading
Derivative [Line Items]
Percentage of derivatives outstanding related to client-related and trading activities	96.00%		96.00%		96.00%
Foreign Currency Denominate
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges			$ 2,800,000
Foreign Currency Denominated Investment Securities
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges			200,000
Available for Sale Investment Securities
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges			$ 100,000