Commitments and Contingencies - Commitments to Extend Credit on Lines of Credit and to Purchase First Mortgages (Details) - Residential real estate - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 3,626	$ 5,025
Home Equity Lines of Credit, Pledged Asset Lines, and Other Lines of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitments to extend credit related to unused HELOCs, PALs, and other lines of credit	3,247	4,533
First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commitments to purchase First Mortgage loans	$ 379	$ 492