Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 469,050	$ 309,471	$ 398,462
Other comprehensive income, net of tax:
Net unrealized Holding Gains (Losses) on Investment Securities	(73,985)	(23,409)	82,204
Reclassification of HTM securities to AFS securities	0	10,938	0
Reclassification to earnings for realized net fixed income securities losses (gains)	(63)	86,023	(6,447)
Reclassification to earnings for net credit-related impairment losses on investment securities	0	0	17
Accretion of securities with noncredit-related impairment losses not expected to be sold	0	0	1,111
Net unrealized losses on other noninterest-bearing investments	2,100	(2,552)	(390)
Net unrealized holding gains (losses) on derivative instruments	4,993	7,455	2,664
Reclassification adjustment for increase in interest income recognized in earnings on derivative instruments	(7,000)	(5,583)	(1,605)
Pension and postretirement	6,986	557	(13,494)
Other comprehensive income	(66,969)	73,429	64,060
Comprehensive income	$ 402,081	$ 382,900	$ 462,522