Bank Loans and Related Allowance for Credit Losses - Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 75	$ 37	$ 73	$ 18
Charge-offs	0	(4)	0	(4)
Recoveries	0	1	0	1
Provision for credit losses	(21)	15	(19)	34
Balance at end of period	54	49	54	49
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	71	34	70	15
Charge-offs	0	0	0	0
Recoveries	0	1	0	1
Provision for credit losses	(22)	11	(21)	30
Balance at end of period	49	46	49	46
Residential real estate | First Mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	68	31	66	13
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	(21)	11	(19)	29
Balance at end of period	47	42	47	42
Residential real estate | HELOCs
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	3	3	4	2
Charge-offs	0	0	0	0
Recoveries	0	1	0	1
Provision for credit losses	(1)	0	(2)	1
Balance at end of period	2	4	2	4
Pledged asset lines
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	0	0	0	0
Charge-offs	0	(4)	0	(4)
Recoveries	0	0	0	0
Provision for credit losses	0	4	0	4
Balance at end of period	0	0	0	0
Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	4	3	3	3
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	1	0	2	0
Balance at end of period	$ 5	$ 3	$ 5	$ 3