Basis of Presentation (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Due from Banks	$ 6,418.5	$ 3,021.0	$ 5,312.1	$ 6,418.5
Federal Reserve and Other Central Bank Deposits			23,035.8	23,695.5
Interest-Bearing Deposits with Banks			$ 6,991.7	6,872.2
Change in Interest-Bearing Deposits with Banks	(56.1)	(3,001.4)
Net Change in Federal Reserve and Other Central Bank Deposits	101.4	1,855.1
Net Cash Used in Investing Activities	(4,930.4)	(7,668.5)
Effect of Foreign Currency Exchange Rates on Cash	208.3	6.6
Increase in Cash and Due from Banks	(1,106.4)	4,095.2
Cash and Due from Banks at Beginning of Year	6,418.5	3,021.0
Cash and Due from Banks at End of Period	5,312.1	7,116.2
Change In Presentation Of Federal Reserve and Foreign Bank Deposits
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Federal Reserve Deposits				0.0
Net Change in Federal Reserve Deposits		0.0
Change In Presentation Of Federal Reserve and Foreign Bank Deposits | Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Due from Banks	6,444.6	3,050.6		6,444.6
Federal Reserve Deposits				16,398.5
Federal Reserve and Other Central Bank Deposits				0.0
Interest-Bearing Deposits with Banks				14,143.1
Change in Interest-Bearing Deposits with Banks		(1,036.1)
Net Change in Federal Reserve Deposits		(102.4)
Net Change in Federal Reserve and Other Central Bank Deposits		0.0
Net Cash Used in Investing Activities		(7,660.7)
Effect of Foreign Currency Exchange Rates on Cash		5.9
Increase in Cash and Due from Banks		4,102.3
Cash and Due from Banks at Beginning of Year	6,444.6	3,050.6
Cash and Due from Banks at End of Period		7,152.9
Change In Presentation Of Federal Reserve and Foreign Bank Deposits | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Due from Banks	(26.1)	(29.6)		(26.1)
Federal Reserve Deposits				(16,398.5)
Federal Reserve and Other Central Bank Deposits				23,695.5
Interest-Bearing Deposits with Banks				$ (7,270.9)
Change in Interest-Bearing Deposits with Banks		(1,965.3)
Net Change in Federal Reserve Deposits		(102.4)
Net Change in Federal Reserve and Other Central Bank Deposits		(1,855.1)
Net Cash Used in Investing Activities		(7.8)
Effect of Foreign Currency Exchange Rates on Cash		0.7
Increase in Cash and Due from Banks		(7.1)
Cash and Due from Banks at Beginning of Year	$ (26.1)	(29.6)
Cash and Due from Banks at End of Period		$ (36.7)