Fair Value Measurements - Unobservable inputs used in determining fair value of embedded derivatives (Details) - Embedded derivatives	12 Months Ended
	Dec. 31, 2018
Unobservable inputs used by management in determining fair value of embedded derivatives
Risk margin for uncertainty in cash flows	0.73%
Minimum
Unobservable inputs used by management in determining fair value of embedded derivatives
Fair Value Input Adjustment for Insurance Subsidiary’s Credit Risk	0.60%
Surrenders	3.00%
Partial surrenders	2.00%
Annuitizations	0.10%
Deaths	1.50%
Budgeted option costs	2.60%
Maximum
Unobservable inputs used by management in determining fair value of embedded derivatives
Fair Value Input Adjustment for Insurance Subsidiary’s Credit Risk	2.10%
Surrenders	23.00%
Partial surrenders	9.00%
Annuitizations	1.00%
Deaths	9.50%
Budgeted option costs	3.60%