Borrowed Funds (Schedule of Federal Home Loan Bank Advances used in Swap Contracts) (Details) $ in Thousands	Mar. 31, 2020 USD ($)
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 3,514,917
FHLB advances under SWAP contracts, average interest rate	1.12%
Interest Rate Swap
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 3,000,000
FHLB advances under SWAP contracts, average interest rate	1.83%
Interest Rate Swap | Effective Maturity 12 months or less
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 225,000
FHLB advances under SWAP contracts, average interest rate	1.28%
Interest Rate Swap | Effective Maturity 13 to 24 months
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 675,000
FHLB advances under SWAP contracts, average interest rate	1.58%
Interest Rate Swap | Effective Maturity 25 to 36 months
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 650,000
FHLB advances under SWAP contracts, average interest rate	1.92%
Interest Rate Swap | Effective Maturity 37 to 48 months
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 200,000
FHLB advances under SWAP contracts, average interest rate	1.97%
Interest Rate Swap | Effective Maturity 49 to 60 months
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 450,000
FHLB advances under SWAP contracts, average interest rate	1.54%
Interest Rate Swap | Effective Maturity Over 60 months
FHLB Short-term Debt [Line Items]
FHLB advances maturing in 12 months or less with effective maturities	$ 800,000
FHLB advances under SWAP contracts, average interest rate	2.26%