Employee Benefit Arrangements - Assumptions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate, benefit obligation	3.85%	4.55%
Discount rate, net benefit cost	4.55%	4.81%	4.36%
Expected rate of return on plan assets, net benefit cost	7.50%	7.50%	7.50%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate, benefit obligation	3.64%	4.55%
Discount rate, net benefit cost	4.55%	4.81%	4.36%
Trend rate assumed for next year	7.00%
Ultimate health care cost trend rate, decrease	5.50%
Health care cost trend rate, period over which rate equals ultimate trend rate	5 years
Ultimate health care cost trend rate	4.50%
Effect on the aggregate of service and interest cost components, One Percentage Point Increase	$ 0
Effect on the aggregate of service and interest cost components, One Percentage Point Decrease	0
Effect on accumulated postretirement benefit obligation, One Percentage Point Increase	1
Effect on accumulated postretirement benefit obligation, One Percentage Point Decrease	$ (1)