Short and Long-term Funding (Details) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2011
Short-term Funding
Federal funds purchased	$ 272,190,000	$ 56,195,000
Securities sold under agreements to repurchase	493,451,000	419,247,000
Federal funds purchased and securities sold under agreements to repurchase	765,641,000	475,442,000
Federal Home Loan Bank ("FHLB") short-term advances	605,000,000	200,000,000
Commercial paper	59,539,000	65,484,000
Other short-term funding	664,539,000	265,484,000
Total short-term funding	1,430,180,000	740,926,000
Long-term Funding
Federal Home Loan Bank long-term advances	2,500,268,000	2,500,297,000
Senior notes , at par	430,000,000	585,000,000
Other long-term funding and capitalized costs	1,279,000	1,970,000
Total long-term funding	2,931,547,000	3,087,267,000
Total short and long-term funding	4,361,727,000	3,828,193,000
Long-term Funding (Textuals) [Abstract]
Weighted average interest rate of Long-term advances	0.10%	0.10%
New senior debt issued			$ 155,000,000	$ 130,000,000	$ 300,000,000
Debt instrument description	reprice at varying intervals, including $1.0 billion repricing at four week intervals, $750 million repricing at 13 week intervals, and $750 million repricing daily
Debt instrument description of variable rate basis	FHLB discount note
Senior Notes [Member]
Long Term Debt Disclosure [Line Items]
Percentage of interest rate on senior notes				5.125%	5.125%