Reinsurance - Account Value, Net Amount at Risk and Contractholders for GMDB Business (Details) - Variable Annuity [Member] - Guaranteed Minimum Death Benefit [Member] Contractholders in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) Contractholders	Dec. 31, 2016 USD ($) Contractholders
Guaranteed Minimum Death Benefits Account Value, Net Amount at Risk And Average Age Table [Line Items]
Account value	$ 10,797	$ 10,650
Net amount at risk	$ 2,187	$ 2,458
Number of contractholders | Contractholders	265,000	285,000