Financing Receivables (Credit Quality Information Tables) (Details 3) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 3,239	$ 3,275
Less: allowance for loan losses	24	26	$ 29	$ 29
Commercial mortgage loans [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	2,708	2,775
Less: allowance for loan losses	19	19
Total loans, net	$ 2,689	$ 2,756
Percentage of gross commercial mortgage loans	100.00%	100.00%
Commercial mortgage loans [Member] | Apartment Building [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 576	$ 566
Percentage of gross commercial mortgage loans	21.00%	20.00%
Commercial mortgage loans [Member] | Hotel [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 39	$ 40
Percentage of gross commercial mortgage loans	1.00%	1.00%
Commercial mortgage loans [Member] | Industrial [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 463	$ 476
Percentage of gross commercial mortgage loans	17.00%	17.00%
Commercial mortgage loans [Member] | Mixed use [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 48	$ 44
Percentage of gross commercial mortgage loans	2.00%	2.00%
Commercial mortgage loans [Member] | Office [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 451	$ 492
Percentage of gross commercial mortgage loans	17.00%	18.00%
Commercial mortgage loans [Member] | Retail [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 912	$ 937
Percentage of gross commercial mortgage loans	34.00%	34.00%
Commercial mortgage loans [Member] | Other [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 219	$ 220
Percentage of gross commercial mortgage loans	8.00%	8.00%
Commercial mortgage loans [Member] | East North Central [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 205	$ 215
Percentage of gross commercial mortgage loans	8.00%	8.00%
Commercial mortgage loans [Member] | East South Central [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 87	$ 90
Percentage of gross commercial mortgage loans	3.00%	3.00%
Commercial mortgage loans [Member] | Middle Atlantic [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 193	$ 192
Percentage of gross commercial mortgage loans	7.00%	7.00%
Commercial mortgage loans [Member] | Mountain [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 245	$ 256
Percentage of gross commercial mortgage loans	9.00%	9.00%
Commercial mortgage loans [Member] | New England [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 64	$ 74
Percentage of gross commercial mortgage loans	2.00%	3.00%
Commercial mortgage loans [Member] | Pacific [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 812	$ 812
Percentage of gross commercial mortgage loans	30.00%	29.00%
Commercial mortgage loans [Member] | South Atlantic [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 742	$ 768
Percentage of gross commercial mortgage loans	28.00%	28.00%
Commercial mortgage loans [Member] | West North Central [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 223	$ 235
Percentage of gross commercial mortgage loans	8.00%	8.00%
Commercial mortgage loans [Member] | West South Central [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 137	$ 133
Percentage of gross commercial mortgage loans	5.00%	5.00%
Syndicated loans [Member]
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Gross	$ 531	$ 498
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Mortgage Loans on Real Estate [Line Items]
Nonperforming loans	17	19
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Syndicated loans [Member]
Mortgage Loans on Real Estate [Line Items]
Nonperforming loans	$ 2	$ 5