Bank Loans and Related Allowance for Credit Losses - Composition of Bank Loans and Delinquency Analysis by Loan Segment (Details) - USD ($)		9 Months Ended	12 Months Ended
		Sep. 30, 2023	Dec. 31, 2022	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Total loans		$ 40,381,000,000	$ 40,578,000,000
Allowance for credit losses		54,000,000	73,000,000	$ 75,000,000	$ 49,000,000	$ 37,000,000	$ 18,000,000
Total bank loans – net	[1]	40,327,000,000	40,505,000,000
Loans accruing interest contractually 90 days or more past due		0	0
Current
Financing Receivable, Past Due [Line Items]
Total loans		40,328,000,000	40,522,000,000
Total past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		53,000,000	56,000,000
30-59 days past due
Financing Receivable, Past Due [Line Items]
Total loans		36,000,000	31,000,000
60-89 days past due
Financing Receivable, Past Due [Line Items]
Total loans		3,000,000	2,000,000
More than or equal to 90 days past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		14,000,000	23,000,000
Residential real estate
Financing Receivable, Past Due [Line Items]
Total loans		26,549,000,000	25,795,000,000
Allowance for credit losses		49,000,000	70,000,000	71,000,000	46,000,000	34,000,000	15,000,000
Total bank loans – net		26,500,000,000	25,725,000,000
Unamortized premiums and discounts and direct origination costs		$ 100,000,000	$ 98,000,000
Residential real estate | Loans Geographic Area | California | Geographic Concentration Risk
Financing Receivable, Past Due [Line Items]
Concentration risk percentage		43.00%	43.00%
Residential real estate | Current
Financing Receivable, Past Due [Line Items]
Total loans		$ 26,509,000,000	$ 25,747,000,000
Residential real estate | Total past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		40,000,000	48,000,000
Residential real estate | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total loans		26,000,000	27,000,000
Residential real estate | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total loans		1,000,000	2,000,000
Residential real estate | More than or equal to 90 days past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		13,000,000	19,000,000
Residential real estate | First Mortgages
Financing Receivable, Past Due [Line Items]
Total loans		26,056,000,000	25,198,000,000
Allowance for credit losses		47,000,000	66,000,000	68,000,000	42,000,000	31,000,000	13,000,000
Total bank loans – net		26,009,000,000	25,132,000,000
Residential real estate | First Mortgages | Current
Financing Receivable, Past Due [Line Items]
Total loans		26,022,000,000	25,157,000,000
Residential real estate | First Mortgages | Total past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		34,000,000	41,000,000
Residential real estate | First Mortgages | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total loans		25,000,000	25,000,000
Residential real estate | First Mortgages | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total loans		1,000,000	2,000,000
Residential real estate | First Mortgages | More than or equal to 90 days past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		8,000,000	14,000,000
Residential real estate | HELOCs
Financing Receivable, Past Due [Line Items]
Total loans		493,000,000	597,000,000
Allowance for credit losses		2,000,000	4,000,000	3,000,000	4,000,000	3,000,000	2,000,000
Total bank loans – net		491,000,000	593,000,000
Residential real estate | HELOCs | Current
Financing Receivable, Past Due [Line Items]
Total loans		487,000,000	590,000,000
Residential real estate | HELOCs | Total past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		6,000,000	7,000,000
Residential real estate | HELOCs | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total loans		1,000,000	2,000,000
Residential real estate | HELOCs | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total loans		0	0
Residential real estate | HELOCs | More than or equal to 90 days past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		5,000,000	5,000,000
Pledged asset lines
Financing Receivable, Past Due [Line Items]
Total loans		13,538,000,000	14,592,000,000
Allowance for credit losses		0	0	0	0	0	0
Total bank loans – net		13,538,000,000	14,592,000,000
Pledged asset lines | Current
Financing Receivable, Past Due [Line Items]
Total loans		13,525,000,000	14,584,000,000
Pledged asset lines | Total past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		13,000,000	8,000,000
Pledged asset lines | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total loans		10,000,000	4,000,000
Pledged asset lines | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total loans		2,000,000	0
Pledged asset lines | More than or equal to 90 days past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		1,000,000	4,000,000
Other
Financing Receivable, Past Due [Line Items]
Total loans		294,000,000	191,000,000
Allowance for credit losses		5,000,000	3,000,000	$ 4,000,000	$ 3,000,000	$ 3,000,000	$ 3,000,000
Total bank loans – net		289,000,000	188,000,000
Other | Current
Financing Receivable, Past Due [Line Items]
Total loans		294,000,000	191,000,000
Other | Total past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		0	0
Other | 30-59 days past due
Financing Receivable, Past Due [Line Items]
Total loans		0	0
Other | 60-89 days past due
Financing Receivable, Past Due [Line Items]
Total loans		0	0
Other | More than or equal to 90 days past due and other nonaccrual loans
Financing Receivable, Past Due [Line Items]
Total loans		$ 0	$ 0

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.