Borrowed Funds - Summary of Borrowed Funds (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Debt Disclosure [Abstract]
FHLB advances	$ 10,312,316	$ 10,872,576
Repurchase agreements	3,425,000	3,425,000
Fed funds purchased	297,000	445,000
Total wholesale borrowings	14,034,316	14,742,576
Junior subordinated debentures	358,296	358,126
Preferred stock of subsidiaries	4,300	4,300
Total other borrowings	362,596	362,426
Total borrowed funds	$ 14,396,912	$ 15,105,002