Derivative and Hedging Activities - Notional Amount and Fair Value of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Derivatives designated as cash flow hedging instruments: | Interest rate swaps on FHLB advances | Cash flow hedging
Liabilities
Notional Amount		$ 5,500
Derivatives designated as cash flow hedging instruments: | Interest rate swaps on FHLB advances | Other Assets | Cash flow hedging
Liabilities
Fair Value		0
Derivatives designated as cash flow hedging instruments: | Interest rate swaps on FHLB advances | Other Liabilities | Cash flow hedging
Liabilities
Fair Value		2
Derivatives designated as cash flow hedging instruments: | Interest rate swaps on multi-family loans held for investment | Fair value hedging
Liabilities
Notional Amount		2,000
Derivatives designated as cash flow hedging instruments: | Interest rate swaps on multi-family loans held for investment | Other Assets | Fair value hedging
Liabilities
Fair Value		0
Derivatives designated as cash flow hedging instruments: | Interest rate swaps on multi-family loans held for investment | Other Liabilities | Fair value hedging
Liabilities
Fair Value		1
Interest rate swaps on multi-family loans held for investment | Mortgage-backed securities forwards | Other Assets
Assets
Notional Amount	$ 186	1,012
Fair Value	7	11
Liabilities
Fair Value	0	0
Interest rate swaps on multi-family loans held for investment | Mortgage-backed securities forwards | Other Liabilities
Assets
Fair Value	0	0
Liabilities
Notional Amount	158	1,048
Fair Value	2	32
Interest rate swaps on multi-family loans held for investment | Rate lock commitments | Other Assets
Assets
Notional Amount	476	1,490
Fair Value	3	12
Liabilities
Fair Value	0	0
Interest rate swaps on multi-family loans held for investment | Rate lock commitments | Other Liabilities
Assets
Fair Value	0	0
Liabilities
Notional Amount	87	77
Fair Value	3	3
Interest rate swaps on multi-family loans held for investment | Interest rate swaps and swaptions | Other Assets
Assets
Notional Amount	1,541	5,431
Fair Value	15	115
Liabilities
Fair Value	0	0
Interest rate swaps on multi-family loans held for investment | Interest rate swaps and swaptions | Other Liabilities
Assets
Fair Value	0	0
Liabilities
Notional Amount	1,782	2,720
Fair Value	$ 30	59
Interest rate swaps on multi-family loans held for investment | Futures | Other Assets
Liabilities
Fair Value		0
Interest rate swaps on multi-family loans held for investment | Futures | Other Liabilities
Liabilities
Notional Amount		2,235
Fair Value		$ 1