Reinsurance - Account Value, Net Amount at Risk and Contractholders for GMDB Business (Details) - Variable Annuity [Member] - Guaranteed Minimum Death Benefit [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Contractholders	Dec. 31, 2017 USD ($) Contractholders
Guaranteed Minimum Death Benefits Account Value, Net Amount at Risk And Average Age Table [Line Items]
Account value	$ 8,402	$ 10,109
Net amount at risk	$ 2,466	$ 2,112
Average attained age of contractholders (weighted by exposure)	74 years	75 years
Number of contractholders | Contractholders	220,000	245,000