Basis of Presentation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Due from Banks	$ 4,892.7	$ 4,445.1	$ 6,418.5	$ 3,021.0	$ 4,892.7	$ 6,418.5
Federal Reserve Deposits						0.0
Federal Reserve and Other Central Bank Deposits					22,208.7	23,695.5
Interest-Bearing Deposits with Banks					$ 5,855.8	6,872.2
Change in Interest-Bearing Deposits with Banks			1,136.3	(1,399.9)
Net Change in Federal Reserve Deposits				0.0
Net Change in Federal Reserve and Other Central Bank Deposits			789.7	(3,239.8)
Net Cash Used in Investing Activities			(5,252.7)	(10,523.3)
Effect of Foreign Currency Exchange Rates on Cash			233.9	(105.8)
Increase in Cash and Due from Banks			(1,525.8)	1,424.1
Cash and Due from Banks at Beginning of Year			6,418.5	3,021.0
Cash and Due from Banks at End of Period	4,892.7	4,445.1	4,892.7	4,445.1
Interest-Bearing Due from and Deposits with Banks	15.4	22.1	49.4	64.9
Federal Reserve and Other Central Bank Deposits	$ 26.2	14.3	83.8	47.9
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		4,485.9	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				238.7
Net Change in Federal Reserve Deposits				(4,865.7)
Net Change in Federal Reserve and Other Central Bank Deposits				0.0
Net Cash Used in Investing Activities				(10,510.6)
Effect of Foreign Currency Exchange Rates on Cash				(107.3)
Increase in Cash and Due from Banks				1,435.3
Cash and Due from Banks at Beginning of Year			6,444.6	3,050.6
Cash and Due from Banks at End of Period		4,485.9		4,485.9
Interest-Bearing Due from and Deposits with Banks		27.0		82.3
Federal Reserve and Other Central Bank Deposits		9.4		30.5
Change In Presentation Of Federal Reserve and Foreign Bank Deposits | Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and Due from Banks		(40.8)	(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				(1,638.6)
Net Change in Federal Reserve Deposits				(4,865.7)
Net Change in Federal Reserve and Other Central Bank Deposits				3,239.8
Net Cash Used in Investing Activities				(12.7)
Effect of Foreign Currency Exchange Rates on Cash				1.5
Increase in Cash and Due from Banks				(11.2)
Cash and Due from Banks at Beginning of Year			$ (26.1)	(29.6)
Cash and Due from Banks at End of Period		(40.8)		(40.8)
Interest-Bearing Due from and Deposits with Banks		(4.9)		(17.4)
Federal Reserve and Other Central Bank Deposits		$ 4.9		$ 17.4