CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Cash pledged as collateral	$ 924,891	$ 579,213
Securities, pledged assets	84,613,575	84,752,790
Loans, pledged assets	2,519,340	1,811,062
Mortgage servicing rights, pledged assets	$ 2,958	$ 5,224
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Cumulative redeemable preferred stock, shares authorized (in shares)	75,950,000	70,700,000
Cumulative redeemable preferred stock, shares issued (in shares)	73,400,000	70,700,000
Cumulative redeemable preferred stock, shares outstanding (in shares)	73,400,000	70,700,000
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	1,924,050,000	1,929,300,000
Common Stock, shares issued (in shares)	1,303,079,555	1,159,585,078
Common Stock, shares outstanding (in shares)	1,303,079,555	1,159,585,078