Bank Loans and Related Allowance for Loan Losses (Changes in Allowance for Loan Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 26	$ 33	$ 26	$ 31
Charge-offs	(2)	0	(2)	(1)
Recoveries	2	0	2	1
Provision for loan losses	0	(2)	0	0
Balance at end of period	26	31	26	31
Residential real estate mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	17	21	17	20
Charge-offs	(1)	0	(1)	(1)
Recoveries	1	0	1	1
Provision for loan losses	0	(1)	0	0
Balance at end of period	17	20	17	20
Home equity loans and lines of credit [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	8	11	8	11
Charge-offs	(1)	0	(1)	0
Recoveries	1	0	1	0
Provision for loan losses	0	(1)	0	(1)
Balance at end of period	8	10	8	10
Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	1	1	1	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision for loan losses	0	0	0	1
Balance at end of period	$ 1	$ 1	$ 1	$ 1