Components of Net Interest Income (Parenthetical) (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Net Interest Income [Line Items]
Cash and Due from Banks	$ 7,152.9	$ 3,050.6	$ 3,945.2	$ 3,162.4
Interest-Bearing Deposits with Banks	15,650.3	$ 14,928.3
Cash and Due from Banks of which interest income earned on for the three months ended June 30, 2015 | Bank Time Deposits
Net Interest Income [Line Items]
Cash and Due from Banks	1,100.0
Cash and Due from Banks of which interest income earned on for the six months ended June 30, 2015 | Bank Time Deposits
Net Interest Income [Line Items]
Cash and Due from Banks	$ 3,300.0