Bank Loans and Related Allowance for Credit Losses - Credit Quality Indicators of Bank Loan Portfolio (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Gross charge-offs
Total loans	$ 0	$ 4	$ 0	$ 4
Residential real estate
Gross charge-offs
Total loans	0	0	0	0
Residential real estate | First Mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2,197		2,197
2022	6,161		6,161		$ 6,444
2021	11,771		11,771		12,293
2020	4,038		4,038		4,270
2019	870		870		929
pre-2019	1,019		1,019		1,262
Total loans	26,056		26,056		$ 25,198
Gross charge-offs
2023			0
2022			0
2021			0
2020			0
2019			0
pre-2019			0
Total loans	$ 0	0	$ 0	0
Percent of Loans on Nonaccrual Status
2023	0.01%		0.01%
2022	0.03%		0.03%		0.02%
2021	0.02%		0.02%		0.03%
2020	0.01%		0.01%		0.09%
2019	0.01%		0.01%		0.02%
pre-2019	0.33%		0.33%		0.43%
Total loans	0.03%		0.03%		0.06%
Residential real estate | First Mortgages | Estimated Current Loan To Value Ratio 70% and Below
Financing Receivable, Credit Quality Indicator [Line Items]
2023	$ 1,517		$ 1,517
2022	4,858		4,858		$ 4,574
2021	11,511		11,511		11,751
2020	4,026		4,026		4,255
2019	868		868		928
pre-2019	1,018		1,018		1,257
Total loans	23,798		23,798		22,765
Residential real estate | First Mortgages | Estimated Current Loan To Value Ratio Greater Than 70% Through 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	680		680
2022	1,283		1,283		1,845
2021	257		257		542
2020	12		12		15
2019	2		2		1
pre-2019	1		1		5
Total loans	2,235		2,235		2,408
Residential real estate | First Mortgages | Estimated Current LTV Greater Than 90% Through 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0		0
2022	19		19		25
2021	3		3		0
2020	0		0		0
2019	0		0		0
pre-2019	0		0		0
Total loans	22		22		25
Residential real estate | First Mortgages | Estimated Current LTV Greater Than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0		0
2022	1		1		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
pre-2019	0		0		0
Total loans	1		1		0
Residential real estate | First Mortgages | Updated FICO Score Below 620
Financing Receivable, Credit Quality Indicator [Line Items]
2023	4		4
2022	10		10		11
2021	11		11		12
2020	6		6		7
2019	2		2		2
pre-2019	12		12		13
Total loans	45		45		45
Residential real estate | First Mortgages | Updated FICO Score 620 Through 679
Financing Receivable, Credit Quality Indicator [Line Items]
2023	26		26
2022	68		68		87
2021	91		91		127
2020	30		30		42
2019	11		11		10
pre-2019	35		35		43
Total loans	261		261		309
Residential real estate | First Mortgages | Updated FICO Score 680 Through 739
Financing Receivable, Credit Quality Indicator [Line Items]
2023	259		259
2022	585		585		711
2021	961		961		1,079
2020	329		329		378
2019	62		62		89
pre-2019	118		118		161
Total loans	2,314		2,314		2,418
Residential real estate | First Mortgages | Updated FICO Score 740 and Above
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1,908		1,908
2022	5,498		5,498		5,635
2021	10,708		10,708		11,075
2020	3,673		3,673		3,843
2019	795		795		828
pre-2019	854		854		1,045
Total loans	23,436		23,436		22,426
Residential real estate | First Mortgages | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
2023	2,197		2,197
2022	6,161		6,161		6,444
2021	11,771		11,771		12,293
2020	4,038		4,038		4,270
2019	870		870		929
pre-2019	1,019		1,019		1,262
Total loans	26,056		26,056		25,198
Residential real estate | First Mortgages | Financial Asset Originated | Origination Loan to Value Ratio 70% and Below
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1,481		1,481
2022	4,561		4,561		4,771
2021	10,197		10,197		10,641
2020	3,357		3,357		3,549
2019	703		703		749
pre-2019	759		759		940
Total loans	21,058		21,058		20,650
Residential real estate | First Mortgages | Financial Asset Originated | Origination Loan to Value Ratio Greater Than 70% Through 90%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	716		716
2022	1,600		1,600		1,673
2021	1,574		1,574		1,652
2020	681		681		721
2019	167		167		180
pre-2019	258		258		320
Total loans	4,996		4,996		4,546
Residential real estate | First Mortgages | Financial Asset Originated | Origination Loan to Value Ratio Greater Than 90% Through 100%
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
pre-2019	2		2		2
Total loans	2		2		2
Residential real estate | First Mortgages | Financial Asset Originated | Origination FICO Score Below 620
Financing Receivable, Credit Quality Indicator [Line Items]
2023	0		0
2022	3		3		3
2021	1		1		1
2020	0		0		0
2019	0		0		0
pre-2019	1		1		1
Total loans	5		5		5
Residential real estate | First Mortgages | Financial Asset Originated | Origination FICO Score 620 Through 679
Financing Receivable, Credit Quality Indicator [Line Items]
2023	3		3
2022	27		27		28
2021	30		30		31
2020	20		20		21
2019	2		2		2
pre-2019	13		13		15
Total loans	95		95		97
Residential real estate | First Mortgages | Financial Asset Originated | Origination FICO Score 680 Through 739
Financing Receivable, Credit Quality Indicator [Line Items]
2023	243		243
2022	795		795		820
2021	1,177		1,177		1,224
2020	400		400		430
2019	108		108		116
pre-2019	206		206		243
Total loans	2,929		2,929		2,833
Residential real estate | First Mortgages | Financial Asset Originated | Origination FICO Score 740 and Above
Financing Receivable, Credit Quality Indicator [Line Items]
2023	1,951		1,951
2022	5,336		5,336		5,593
2021	10,563		10,563		11,037
2020	3,618		3,618		3,819
2019	760		760		811
pre-2019	799		799		1,003
Total loans	23,027		23,027		22,263
Residential real estate | HELOCs
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	317		317		382
HELOCs converted to term loans	176		176		215
Total loans	493		493		$ 597
Gross charge-offs
Revolving HELOCs amortized cost basis			0
HELOCs converted to term loans			0
Total loans	$ 0	$ 0	$ 0	$ 0
Percent of Loans on Nonaccrual Status
Revolving HELOCs amortized cost basis	0.28%		0.28%		0.34%
HELOCs converted to term loans	2.03%		2.03%		1.90%
Total loans	1.01%		1.01%		0.84%
Residential real estate | HELOCs | Estimated Current Loan To Value Ratio 70% and Below
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	$ 315		$ 315		$ 380
HELOCs converted to term loans	175		175		214
Total loans	490		490		594
Residential real estate | HELOCs | Estimated Current Loan To Value Ratio Greater Than 70% Through 90%
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	2		2		2
HELOCs converted to term loans	1		1		1
Total loans	3		3		3
Residential real estate | HELOCs | Estimated Current LTV Greater Than 90% Through 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0		0		0
HELOCs converted to term loans	0		0		0
Total loans	0		0		0
Residential real estate | HELOCs | Estimated Current LTV Greater Than 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0		0		0
HELOCs converted to term loans	0		0		0
Total loans	0		0		0
Residential real estate | HELOCs | Updated FICO Score Below 620
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	2		2		2
HELOCs converted to term loans	5		5		5
Total loans	7		7		7
Residential real estate | HELOCs | Updated FICO Score 620 Through 679
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	6		6		6
HELOCs converted to term loans	8		8		10
Total loans	14		14		16
Residential real estate | HELOCs | Updated FICO Score 680 Through 739
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	45		45		52
HELOCs converted to term loans	30		30		35
Total loans	75		75		87
Residential real estate | HELOCs | Updated FICO Score 740 and Above
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	264		264		322
HELOCs converted to term loans	133		133		165
Total loans	397		397		487
Residential real estate | HELOCs | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	317		317		382
HELOCs converted to term loans	176		176		215
Total loans	493		493		597
Residential real estate | HELOCs | Financial Asset Originated | Origination Loan to Value Ratio 70% and Below
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	282		282		332
HELOCs converted to term loans	123		123		153
Total loans	405		405		485
Residential real estate | HELOCs | Financial Asset Originated | Origination Loan to Value Ratio Greater Than 70% Through 90%
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	35		35		50
HELOCs converted to term loans	52		52		61
Total loans	87		87		111
Residential real estate | HELOCs | Financial Asset Originated | Origination Loan to Value Ratio Greater Than 90% Through 100%
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0		0		0
HELOCs converted to term loans	1		1		1
Total loans	1		1		1
Residential real estate | HELOCs | Financial Asset Originated | Origination FICO Score Below 620
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0		0		0
HELOCs converted to term loans	0		0		0
Total loans	0		0		0
Residential real estate | HELOCs | Financial Asset Originated | Origination FICO Score 620 Through 679
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0		0		0
HELOCs converted to term loans	1		1		2
Total loans	1		1		2
Residential real estate | HELOCs | Financial Asset Originated | Origination FICO Score 680 Through 739
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	53		53		59
HELOCs converted to term loans	39		39		47
Total loans	92		92		106
Residential real estate | HELOCs | Financial Asset Originated | Origination FICO Score 740 and Above
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	264		264		323
HELOCs converted to term loans	136		136		166
Total loans	$ 400		$ 400		$ 489