Short-Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Ending Balance	$ 4,782,798	$ 3,675,227
Average Balance	4,814,393	1,320,900
Maximum Outstanding Balance	6,190,544	3,942,343
Federal funds purchased
Short-term Debt [Line Items]
Ending Balance	$ 673,545	$ 693,819
Ending Average Interest Rate	0.37%	0.27%
Average Balance	$ 692,737	$ 722,753
Maximum Outstanding Balance	975,785	960,935
Securities sold under agreements to repurchase
Short-term Debt [Line Items]
Ending Balance	$ 76,609	$ 435,684
Ending Average Interest Rate	0.44%	0.73%
Average Balance	$ 114,940	$ 212,686
Maximum Outstanding Balance	232,605	435,684
Total federal funds purchased and securities sold under agreements to repurchase
Short-term Debt [Line Items]
Ending Balance	750,154	1,129,503
Average Balance	807,677	935,439
Maximum Outstanding Balance	1,208,390	1,396,619
Other short-term borrowings
Short-term Debt [Line Items]
Ending Balance	$ 4,032,644	$ 2,545,724
Ending Average Interest Rate	1.34%	1.62%
Average Balance	$ 4,006,716	$ 385,461
Maximum Outstanding Balance	$ 4,982,154	$ 2,545,724