Long-term Funding, Composition (Details) - USD ($) $ in Thousands	1 Months Ended
	Nov. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2011	Mar. 31, 2011
Long-term Funding
FHLB advances		$ 1,750,225	$ 3,000,260
Senior notes, at par		680,000	680,000
Subordinated notes, at par		250,000	250,000
Other Long-term Debt and Capitalized Costs		(875)	(143)
Total long-term funding		$ 2,679,350	$ 3,930,117
Long Term Debt Disclosure [Line Items]
Percentage of interest rate on senior notes	2.75%
Long-term Funding (Textuals) [Abstract]
Weighted average interest rate of Long-term advances		0.24%	0.11%
Long-term FHLB Advances		$ 5,500,000
New senior debt issued	$ 250,000			$ 130,000	$ 300,000
Subordinated debentures issued	$ 250,000
Fixed coupon interest rate of subordinated debt	4.25%
Total Federal Home Loan Bank Advances		$ 2,100,000
Senior Notes [Member]
Long Term Debt Disclosure [Line Items]
Percentage of interest rate on senior notes					5.125%