Bank Loans and Related Allowance for Credit Losses - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 15
Accrued interest	161	$ 157
Residential real estate | First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans	$ 21,600
Percent of loans with interest-only payments	27.00%
Percent of interest only adjustable rate	84.00%
Total bank loans	$ 26,201	26,153
Residential real estate | First Mortgages | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fixed rate interest rate period	3 years
Interest-only reset period	3 years
Residential real estate | First Mortgages | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fixed rate interest rate period	10 years
Residential real estate | HELOCs
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan term	30 years
Initial draw period	10 years
Converting to amortizing loans period	20 years
Total bank loans	$ 455	$ 479
Percent of loan balance outstanding, borrowers paid only minimum due	59.00%
Residential real estate | Home Equity Secured By Second Liens
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total bank loans	$ 360