Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Restricted cash and due from banks	$ 114.9	$ 176.1
Restricted interest-bearing deposits	93.6	102.8
Securities carried at fair value with changes recorded in net income	255.6	283.5
Other assets at fair value	79.4	111.6
Other liabilities at fair value	225.4	177.9
Borrowings contractually due within twelve months	$ 250.6	$ 2,321.7
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0
Preferred Stock, shares authorized	100,000,000	0
Preferred Stock, shares issued	325,000	0
Preferred Stock, shares outstanding	325,000	0
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	600,000,000	600,000,000
Common Stock, shares issued	207,336,689	206,182,213
Common Stock, shares outstanding	135,418,595	202,087,672
Treasury stock, shares at cost	71,918,094	4,094,541