Reinsurance Reinsurance (Net Amount at Risk and 100 Percent Mortality) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Guaranteed Minimum Benefits [Line Items]
Unpaid losses and loss expenses	$ 62,960	$ 63,179	$ 60,540	$ 37,303
Average attained age of all policyholders under all benefits reinsured, years	71 years
GLB
Guaranteed Minimum Benefits [Line Items]
Net Amount at Risk	$ 1,233	691
GMDB
Guaranteed Minimum Benefits [Line Items]
Net Amount at Risk	$ 408	279
Mortality percentage according to Annuity 2000 mortality table	100.00%
GMDB with Both Risk(GMDB and GLB) [Member]
Guaranteed Minimum Benefits [Line Items]
Net Amount at Risk	$ 103	81
GLB with Both Risk(GLB and GMDB) [Member]
Guaranteed Minimum Benefits [Line Items]
Net Amount at Risk	$ 517	$ 392
Minimum | GLB
Guaranteed Minimum Benefits [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate	4.00%
Minimum | GMDB
Guaranteed Minimum Benefits [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate	3.30%
Minimum | GLB with Both Risk(GLB and GMDB) [Member]
Guaranteed Minimum Benefits [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate	4.00%
Maximum | GLB
Guaranteed Minimum Benefits [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate	4.30%
Maximum | GMDB
Guaranteed Minimum Benefits [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate	3.50%
Maximum | GLB with Both Risk(GLB and GMDB) [Member]
Guaranteed Minimum Benefits [Line Items]
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate	4.30%
Measurement Input, Mortality Rate [Member] | GMDB
Guaranteed Minimum Benefits [Line Items]
Unpaid losses and loss expenses	$ 177
Measurement Input, Mortality Rate [Member] | GMDB with Both Risk(GMDB and GLB) [Member]
Guaranteed Minimum Benefits [Line Items]
Unpaid losses and loss expenses	$ 18