Bank Loans and Related Allowance for Credit Losses (Credit Quality Indicators of Bank Loan Portfolio) (Details) $ in Millions	Sep. 30, 2021 USD ($) credit_rating	Dec. 31, 2020 USD ($) credit_rating
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 31,583	$ 23,843
First Mortgage [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	9,775
2020	5,803	7,974
2019	1,465	2,820
2018	270	557
2017	549	1,047
pre-2017	1,428	2,506
Total loans	$ 19,290	$ 14,904
Percent of Loans on Nonaccrual Status
2021	0.05%
2020	0.12%	0.09%
2019	0.14%	0.38%
2018	0.33%	1.02%
2017	0.36%	0.87%
pre-2017	1.31%	1.57%
Percent of Loans on Nonaccrual Status	0.19%	0.48%
First Mortgage [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 9,775
2020	5,803	$ 7,974
2019	1,465	2,820
2018	270	557
2017	549	1,047
pre-2017	1,428	2,506
Total loans	19,290	14,904
First Mortgage [Member] | Origination Loan to Value Ratio 70% and Below [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	8,464
2020	4,838	6,653
2019	1,161	2,211
2018	202	396
2017	417	793
pre-2017	1,065	1,935
Total loans	16,147	11,988
First Mortgage [Member] | Origination Loan to Value Ratio Greater Than 70% Through 90% [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	1,311
2020	965	1,321
2019	304	609
2018	68	161
2017	132	254
pre-2017	360	568
Total loans	3,140	2,913
First Mortgage [Member] | Origination Loan to Value Ratio Greater Than 90% Through 100% [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
pre-2017	3	3
Total loans	3	3
First Mortgage [Member] | Estimated Current Loan To Value Ratio 70% and Below [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	8,857
2020	5,727	6,999
2019	1,451	2,582
2018	268	533
2017	547	1,034
pre-2017	1,426	2,490
Total loans	18,276	13,638
First Mortgage [Member] | Estimated Current Loan To Value Ratio Greater Than 70% Through 90% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	918
2020	76	975
2019	14	238
2018	2	24
2017	2	13
pre-2017	2	16
Total loans	1,014	1,266
First Mortgage [Member] | Estimated Current LTV Greater Than 90% Through 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
pre-2017	0	0
Total loans	0	0
First Mortgage [Member] | Estimated Current LTV Greater Than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0	0
2019	0	0
2018	0	0
2017	0	0
pre-2017	0	0
Total loans	0	0
First Mortgage [Member] | Origination FICO Score Below 620 [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	1	1
2019	0	0
2018	0	0
2017	0	0
pre-2017	1	2
Total loans	2	3
First Mortgage [Member] | Origination FICO Score 620 Through 679 [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	21
2020	28	29
2019	5	13
2018	1	3
2017	7	8
pre-2017	21	31
Total loans	83	84
First Mortgage [Member] | Origination FICO Score 680 Through 739 [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	934
2020	611	794
2019	179	355
2018	51	105
2017	112	181
pre-2017	256	419
Total loans	2,143	1,854
First Mortgage [Member] | Origination FICO Score 740 and Above [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	8,820
2020	5,163	7,150
2019	1,281	2,452
2018	218	449
2017	430	858
pre-2017	1,150	2,054
Total loans	17,062	12,963
First Mortgage [Member] | Weighted Average Updated FICO Score Below 620 [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	4
2020	4	5
2019	2	2
2018	0	1
2017	3	4
pre-2017	13	19
Total loans	26	31
First Mortgage [Member] | Wighted Average Updated FICO Score 620 Through 679 [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	76
2020	76	67
2019	20	34
2018	7	16
2017	9	21
pre-2017	35	60
Total loans	223	198
First Mortgage [Member] | Weighted Average Updated FICO Score 680 Through 739 [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	882
2020	486	784
2019	145	252
2018	33	66
2017	63	121
pre-2017	171	281
Total loans	1,780	1,504
First Mortgage [Member] | Weighted Average Updated FICO Score 740 and Above [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2021	8,813
2020	5,237	7,118
2019	1,298	2,532
2018	230	474
2017	474	901
pre-2017	1,209	2,146
Total loans	17,261	13,171
HELOCs [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	388	463
HELOCs converted to term loans	300	379
Total loans	$ 688	$ 842
Percent of Loans on Nonaccrual Status
Revolving HELOCs amortized cost basis	0.86%	1.37%
HELOCs converted to term loans	2.48%	2.80%
Percent of Loans on Nonaccrual Status	1.60%	2.02%
HELOCs [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	$ 388	$ 463
HELOCs converted to term loans	300	379
Total loans	688	842
HELOCs [Member] | Origination Loan to Value Ratio 70% and Below [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	315	351
HELOCs converted to term loans	214	269
Total loans	529	620
HELOCs [Member] | Origination Loan to Value Ratio Greater Than 70% Through 90% [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	73	112
HELOCs converted to term loans	84	107
Total loans	157	219
HELOCs [Member] | Origination Loan to Value Ratio Greater Than 90% Through 100% [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	2	3
Total loans	2	3
HELOCs [Member] | Estimated Current Loan To Value Ratio 70% and Below [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	387	452
HELOCs converted to term loans	296	368
Total loans	683	820
HELOCs [Member] | Estimated Current Loan To Value Ratio Greater Than 70% Through 90% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	1	11
HELOCs converted to term loans	3	9
Total loans	4	20
HELOCs [Member] | Estimated Current LTV Greater Than 90% Through 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	1	1
Total loans	1	1
HELOCs [Member] | Estimated Current LTV Greater Than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	0	1
Total loans	0	1
HELOCs [Member] | Origination FICO Score Below 620 [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0	0
HELOCs converted to term loans	0	0
Total loans	0	0
HELOCs [Member] | Origination FICO Score 620 Through 679 [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	0	1
HELOCs converted to term loans	3	3
Total loans	3	4
HELOCs [Member] | Origination FICO Score 680 Through 739 [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	65	82
HELOCs converted to term loans	63	80
Total loans	128	162
HELOCs [Member] | Origination FICO Score 740 and Above [Member] | Financial Asset Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	323	380
HELOCs converted to term loans	234	296
Total loans	557	676
HELOCs [Member] | Weighted Average Updated FICO Score Below 620 [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	2	3
HELOCs converted to term loans	7	9
Total loans	9	12
HELOCs [Member] | Wighted Average Updated FICO Score 620 Through 679 [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	8	12
HELOCs converted to term loans	14	20
Total loans	22	32
HELOCs [Member] | Weighted Average Updated FICO Score 680 Through 739 [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	53	58
HELOCs converted to term loans	42	55
Total loans	95	113
HELOCs [Member] | Weighted Average Updated FICO Score 740 and Above [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving HELOCs amortized cost basis	325	390
HELOCs converted to term loans	237	295
Total loans	562	685
Pledged Asset Lines [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	11,412	7,916
Pledged Asset Lines [Member] | Weighted Average Loan to Value Ratio =70% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 11,412	$ 7,916
Percent of Loans on Nonaccrual Status
Percent of Loans on Nonaccrual Status	0.00%	0.00%
Weighted Average Updated FICO | credit_rating	768	770