Short and Long-term Funding FHLB Maturity Schedule (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 3,180,967	$ 3,574,371
Weighted Average Coupon Rate	2.20%	2.19%
Maturity or put date 1 year or less
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 2,055,056	$ 2,262,584
Weighted Average Coupon Rate	2.19%	2.06%
After 1 but within 2
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 14,099	$ 1,285,039
Weighted Average Coupon Rate	2.95%	2.39%
After 2 but within 3
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 504,154	$ 14,393
Weighted Average Coupon Rate	2.12%	2.98%
After 3 years
FHLB_Maturity_ [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 607,657	$ 12,354
Weighted Average Coupon Rate	2.29%	4.55%