Consolidated Balance Sheet (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Pledged securities that can be sold or repledged	$ 487,151,000	$ 1,203,473,000
Investment securities, available for sale, amortized cost	10,938,796,000	13,338,301,000
Investment securities, held to maturity, fair value	3,341,762,000	2,451,222,000
Other, fair value	$ 415,028,000	$ 461,118,000
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	1,000,000	1,000,000
Common stock, par value	$ 0.50	$ 0.50
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	159,817,518	159,945,678
Common stock issuable, shares	27,138	32,403
Treasury stock, common shares	9,733,115	3,764,742
Series A and Series C [Member]
Preferred stock, shares issued	731,500	731,500
Preferred stock, shares outstanding	731,500	731,500
Preferred stock, liquidation preference per share	$ 1,000	$ 1,000
Series D Preferred Stock [Member]
Preferred stock, shares issued	50,000	50,000
Preferred stock, shares outstanding	50,000	50,000
Preferred stock, liquidation preference per share	$ 10,000	$ 10,000