Short and Long-Term Funding (Components of Short-term and Long-term Funding) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Short-term Funding [Abstract]
Federal funds purchased	$ 69,085	$ 141,950
Securities sold under agreements to repurchase	214,869	182,865
Federal funds purchased and securities sold under agreements to repurchase	283,954	324,815
FHLB advances	1,780,000	284,000
Commercial paper	82,420	67,467
Other short-term funding	1,862,420	351,467
Total short-term funding	2,146,374	676,282
Long-term Funding
FHLB advances	2,735,887	2,900,168
Senior notes, at par	250,000	250,000
Subordinated notes, at par	250,000	250,000
Other long-term funding and capitalized costs	(2,549)	(2,718)
Total long-term funding	3,233,338	3,397,450
Total short and long-term funding	$ 5,379,712	$ 4,073,732