Bank Loans and Related Allowance for Credit Losses - Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 73	$ 18	$ 30
Charge-offs	0	(4)	(1)
Recoveries	0	1	1
Provision for loan losses	(35)	58	(12)
Balance at end of period	38	73	18
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	70	15	27
Charge-offs	0	0	0
Recoveries	0	1	1
Provision for loan losses	(36)	54	(13)
Balance at end of period	34	70	15
Pledged asset lines
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	0	0	0
Charge-offs	0	(4)	0
Recoveries	0	0	0
Provision for loan losses	0	4	0
Balance at end of period	0	0	0
Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	3	3	3
Charge-offs	0	0	(1)
Recoveries	0	0	0
Provision for loan losses	1	0	1
Balance at end of period	4	3	3
First Mortgages | Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	66	13	22
Charge-offs	0	0	0
Recoveries	0	0	0
Provision for loan losses	(34)	53	(9)
Balance at end of period	32	66	13
HELOCs | Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	4	2	5
Charge-offs	0	0	0
Recoveries	0	1	1
Provision for loan losses	(2)	1	(4)
Balance at end of period	$ 2	$ 4	$ 2