Bank Loans and Related Allowance for Loan Losses (Credit Quality Indicators of Bank Loan Portfolio) (Details) $ in Millions	Dec. 31, 2017 USD ($) credit_rating	Dec. 31, 2016 USD ($) credit_rating
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 16,504	$ 15,429
First Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 10,016	$ 9,134
Weighted Average Updated FICO | credit_rating	775	773
Percent of Loans that are on Nonaccrual Status	0.14%	0.10%
First Mortgage [Member] | Origination FICO Score Below 620 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 6	$ 8
First Mortgage [Member] | Origination FICO Score 620 Through 679 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	89	92
First Mortgage [Member] | Origination FICO Score 680 Through 739 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	1,569	1,427
First Mortgage [Member] | Origination FICO Score 740 And Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	8,352	7,607
First Mortgage [Member] | Year of origination Pre 2013 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	1,478	2,136
First Mortgage [Member] | Year of origination 2013 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	1,326	1,746
First Mortgage [Member] | Year of origination 2014 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	530	685
First Mortgage [Member] | Year of origination 2015 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	1,218	1,458
First Mortgage [Member] | Year of origination 2016 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	2,886	3,109
First Mortgage [Member] | Year of origination 2017 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	2,578
First Mortgage [Member] | Estimated Current LTV 70% And Below [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 9,046	$ 8,350
Weighted Average Updated FICO | credit_rating	775	774
Percent of Loans that are on Nonaccrual Status	0.09%	0.04%
First Mortgage [Member] | Estimated Current LTV Greater Than 70% through 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 961	$ 743
Weighted Average Updated FICO | credit_rating	769	768
Percent of Loans that are on Nonaccrual Status	0.46%	0.35%
First Mortgage [Member] | Estimated Current LTV Greater Than 90% through 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 5	$ 21
Weighted Average Updated FICO | credit_rating	714	747
Percent of Loans that are on Nonaccrual Status	10.49%	2.08%
First Mortgage [Member] | Estimated Current LTV Greater Than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 4	$ 20
Weighted Average Updated FICO | credit_rating	713	709
Percent of Loans that are on Nonaccrual Status	6.23%	14.50%
First Mortgage [Member] | Origination Loan To Value Ratio 70% And Below [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 7,569	$ 6,865
First Mortgage [Member] | Origination Loan to Value Ratio Greater Than 70% Through 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	2,441	2,260
First Mortgage [Member] | Origination Loan to Value Ratio Greater Than 90% Through 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	6	9
HELOC's [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 1,943	$ 2,350
Weighted Average Updated FICO | credit_rating	770	769
Utilization Rate	33.00%	36.00%
Percent of Loans that are on Nonaccrual Status	0.27%	0.20%
HELOC's [Member] | Origination FICO Score Below 620 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 1	$ 0
HELOC's [Member] | Origination FICO Score 620 Through 679 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	10	13
HELOC's [Member] | Origination FICO Score 680 Through 739 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	365	432
HELOC's [Member] | Origination FICO Score 740 And Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	1,567	1,905
HELOC's [Member] | Year of origination Pre 2013 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	1,349	1,765
HELOC's [Member] | Year of origination 2013 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	147	193
HELOC's [Member] | Year of origination 2014 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	116	152
HELOC's [Member] | Year of origination 2015 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	128	146
HELOC's [Member] | Year of origination 2016 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	111	94
HELOC's [Member] | Year of origination 2017 [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	92
HELOC's [Member] | Estimated Current LTV 70% And Below [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 1,773	$ 2,070
Weighted Average Updated FICO | credit_rating	772	771
Utilization Rate	32.00%	35.00%
Percent of Loans that are on Nonaccrual Status	0.18%	0.12%
HELOC's [Member] | Estimated Current LTV Greater Than 70% through 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 148	$ 234
Weighted Average Updated FICO | credit_rating	755	757
Utilization Rate	47.00%	50.00%
Percent of Loans that are on Nonaccrual Status	0.84%	0.40%
HELOC's [Member] | Estimated Current LTV Greater Than 90% through 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 14	$ 29
Weighted Average Updated FICO | credit_rating	742	747
Utilization Rate	64.00%	66.00%
Percent of Loans that are on Nonaccrual Status	2.85%	1.74%
HELOC's [Member] | Estimated Current LTV Greater Than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 8	$ 17
Weighted Average Updated FICO | credit_rating	718	728
Utilization Rate	72.00%	70.00%
Percent of Loans that are on Nonaccrual Status	4.91%	3.73%
HELOC's [Member] | Origination Loan To Value Ratio 70% And Below [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 1,360	$ 1,628
HELOC's [Member] | Origination Loan to Value Ratio Greater Than 70% Through 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	574	709
HELOC's [Member] | Origination Loan to Value Ratio Greater Than 90% Through 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	9	13
Pledged asset lines [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	4,369	3,851
Pledged asset lines [Member] | Weighted Average Loan to Value Ratio =70% [Member]
Financing Receivable, Recorded Investment [Line Items]
Balance	$ 4,369	$ 3,851
Weighted Average Updated FICO | credit_rating	765	763
Utilization Rate	41.00%	46.00%
Percent of Loans that are on Nonaccrual Status	0.00%