Guaranteed Benefit Features (Information On Guaranteed Death Benefit Features) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Return of Net Deposits [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total Account Value	[1]	$ 95,959	$ 96,941
Net Amount At Risk	[1],[2]	$ 119	$ 81
Average attained age of contract holders	[1]	64 years	64 years
Minimum Return [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total Account Value	[1]	$ 104	$ 108
Net Amount At Risk	[1],[2]	$ 17	$ 18
Average attained age of contract holders	[1]	76 years	76 years
Guaranteed minimum return	[1]	5.00%	5.00%
Anniversary Contract Value [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total Account Value	[1]	$ 26,071	$ 26,596
Net Amount At Risk	[1],[2]	$ 543	$ 417
Average attained age of contract holders	[1]	70 years	70 years

[1] Our variable contracts with guarantees may offer more than one type of guarantee in each contract; therefore, the amounts listed are not mutually exclusive.

[2] Represents the amount of death benefit in excess of the account balance that is subject to market fluctuations.