Bank Loans and Related Allowance for Credit Losses - Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at March 31, 2024	$ 21	$ 32	$ 21	$ 38	$ 38
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	1	(12)	1	(18)
Balance at June 30, 2024	22	20	22	20	21
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at March 31, 2024	15	28	15	34	34
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	1	(13)	1	(19)
Balance at June 30, 2024	16	15	16	15	15
Residential real estate \| First Mortgages
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at March 31, 2024	14	27	14	32	32
Charge-offs	0	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	1	(13)	1	(18)
Balance at June 30, 2024	15	14	15	14	14
Residential real estate \| HELOCs
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at March 31, 2024	1	1	1	2	2
Charge-offs	0	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	0	0	0	(1)
Balance at June 30, 2024	1	1	1	1	1
Pledged asset lines
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at March 31, 2024	0	0	0	0	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	0	0	0	0
Balance at June 30, 2024	0	0	0	0	0
Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at March 31, 2024	6	4	6	4	4
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for credit losses	0	1	0	1
Balance at June 30, 2024	$ 6	$ 5	$ 6	$ 5	$ 6

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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- Definition

Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

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- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476148/220-40-50-22

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